My understanding of Bitcoin's value is the same as in any other system of exchange. It's the network effect. The more people who are using it, the more valuable it is. It has two things in it: it has good properties as an asset and it's decentralized, which is a huge advantage.
And one of the nice things about it is that it doesn't use a third party, so you don't have to trust anyone with your financial information, which is a very good trait in a system.

And that's really the key to an asset like this.

Prompting you are right as demand affects the price of Bitcoin, yet we can't deny the surge after the market turn to its first Bullish trend. People had valued  Bitcoin more than anything we found in the crypto world and not to wonder why it continue till this time and probably in the future. Granting how the demand is growing, the more possibility that the price of Bitcoin will even grow more...
5-10 years from now we see more changes, that really sure it happens. 

Bitcoin have symbolic value of what people are willing to pay for it. I don't think it's reasonable to measure its 'intrinsic value' in any way, even though I guess it's possible to do that by taking into account the average cost of mining (electricity bills, maintenance, human workforce) per coin, but it's not giving anything helpful, and even produce doesn't have its value counted this way (goods usually cost significantly more than it's worth to make them and, in some cases where state regulation of prices is done, they can cost less). So the demand defines the price, but the demand is heavily affected by sentiments of people (FOMO or FUD).

underlying value comes from the bottom amount absolutely no one can ever aquire it for at the moment.
whether its from selling goods or services for coin.
whether its from buying coin on a market
whether its from mining it.

the bottom VALUE on the planet is about $37k. because no one on the planet can mine it for less. and the market PRICE is at ~$40k and those selling goods/services try to add on a few percent so they get it for a bit more.

other places on the planet have higher mining costs. so instead of mining. they buy it.  if the price is better then their local mining cost, thus supporting the market to be above the cheapest acquisition cost(mining in cheapest region)
then other regions have even higher costs so they are more then happy to keep buying even in high price times

if the PRICE. came down to the value line (bottom cheapest mining cost on planet) even those cheap miners would go on a buy frenzy.. after all why wait hours or days to mine 1btc when you can buy it at near same rate in seconds.

you cannot see this value line on any market chart. sorry its not the price. its an invisible line below the price. and its why people dont know or think there is a value because they dont see everyone showing a line on charts. but the line does exist. and it definitely is no where near $0

all the other stuff about trader sentiment of supply and demand. is what plays in the speculation ABOVE value. its the volatile wobble factor of the price triggered by human nature and emotion.

alot of people try to make the "mining supply limit" thing a price impactor of "supply and demand"

but here is the thing
total supply DOES NOT decrease.

in 2012 there were 10.5m coins
in 2016 there were 15.75m
in 2020 it was 18.375m
and we are sitting at 18.96m
and in 120years it just stops.. and stays at 21m.

the numbers in circulation keep going up. until they stop.

the mining cost (coin mined per block) does affect the underlying value. which then pumps up the bottomline market price. but it does not affect the day to day speculative emotion of price. becase the rate of mining 'supply' only changes once every 4 years. not daily

markets dont even touch all of this supply in circulation. markets only utilise like 10% of supply because not everyone is trading at the same time. the market PRICE "supply" is not affected by mined coins created or the general supply of 18.96m
markets play with a subset of coins normally about a variable of 1.5-4mill coins, but diluted over many different exchanges at any time
also when there is a low market allotment. sellers stop selling 0.1 coin for $4k and start selling 0.01coin for $401.

yep back in 2012 when there were only 10.5 coins total supply. people were making orders for 1-1000 coin
today at near 19m coins. people are making orders for 0.001-1coin. yet "supply" dynamics should be that people make orders for
1.9-1900coins. because of the silly rhetoric of "supply".

the reason why traders now only sell orders of 0.001-1. is not to do with supply of coin. but the fact that the buyers are investing a limited amount of fiat

in 2012 $600 could get you 100 coins. but them same investors only wanting to make buy orders of $600 are now getting only 0.015 coin.
because if seller were to try to off load 1BTC they will take away 66 keen buyers off the bidding table in 1 swoop and cause a price crash
so although there is more general supply than in 2012. the traders within the markets are not putting all that supply into exchanges to cause a crash.
so yea its not a simple "supply" thing. there are many factors involved and not the ones you have been taught at highschool

as for demand. well thats a variety of factors. some of which are that if it costs americans ~$43k and cost a japenese $75k to mine but the price is $40k. dang right they will want to buy and support the price above the bottom value

but here is the thing. the PRICE is not the VALUE.
the value window currently sits at a gap of $37k -$88k
where by EVERYONE would want to buy at $37k
where by NO ONE would want to sell below $37k
 and NO ONE would want to buy at $88k
 and EVERYONE would want to sell at $88k

all because no one can mine for less and no one can mine for more. so the market PRICE sits somewhere inbetween those numbers depending on speculations of emotion, sentiment and person reasons affecting their decisions

its the same with gold.
if gold cost $0.90-$2 to mine gold in your own back yard with a spoon and coffee filter as the cheapest way to mine. at most the market sentiment will allow is $2
because everyone else can probably mine for $2 or less aswell..

but it actually costs gold miners $900/ounce to mine. which is the baseline VALUE and which is why the price is between $900-$2k because its between the window of mining cost. where by no one would buy for $2.1k if everyone on the planet can mine for $2k so no one buys for such high price unless its a hype bubble thats about to crash.
and its why traders know they have no fear of ever seeing gold drop below $900. because if it even got close to $900, everyone would go on buying frenzy for cheap gold and support the price ABOVE value

Bitcoin value created by the community and price depends on the demand. I don't want to mix price and value together. It's because Bitcoin fully backed the community, on the other hand, the price works based on new investors. We can see many cryptocurrencies have been created after Bitcoin, but it's all not appreciated than Bitcoin and the only reason for community acceptance. Also, new instinctual investors enter Bitcoin which has an impact on the price. It's not all about mining Bitcoin.

The value of Bitcoins is basically based on the Demand and supply rule which does mean that the moment the demand exceeds the supply the value will sky rocket. It's not really a weird science but much like stocks it fluctuates in the value, being more volatile bitcoins at the end of the day gains it's power from being an essential asset, also the holders, the long term holders like Mr. Satoshi provides bitcoins, value since the holders are like 50% of the bitcoin investors, I think the value is dependent upon many factors, therefore it's the sum of all of these that makes it valuable. Whales also guarantee a certain amount of backup as well.

What gives bitcoin value most in my eyes is the decentralized electronic nature of a cash system that was never possible before. The limited amount of twenty one million is also a large part of what gives it its value. There had never been anything like it before.

I'll turn the question around: what gives unbacked paper money its worth? The answer is simple: poeple all believe that the paper in front of them is worth $100, even if the material is the same as the $50 bill, which is only half the value. Bitcoin's value is basically similar, except that this value is still defined by the invested energy it took to mine that bitcoin.

I believe its because of alot people that still keep believing and keep supporting bitcoin wherein reason there's a demand and supply in the market and bitcoin price keeps improving and getting matured every year. . Because to be honest i do believe that without strong support in the market for sure bitcoin isn't valuable right now and it's useless in the crypto space..

To make the story short it's because of us  reason why bitcoin has value.