I believe that Satoshi Nakamoto originally meant that Bitcoin will either be widely recognized within 20 years or no one cares about it. It's not that Bitcoin's transaction volume will reach what order of magnitude. I think that Bitcoin in 2029 may exist more as a value calibration, just like the digital gold that people often say. By then, Bitcoin's transaction volume may not be very large, but its influence has penetrated into all aspects of people's lives.

You don't need to look far beyond, you just have to observed how large the volume is today in 2021 and say that obviously, the transaction will increase in time. And by that time, "almost all bitcoin" are going to be mined, so the supply and dwindling, but the demand will still be there that can push the price and obviously the transaction volumes.

When Satoshi said in the next 20 years bitcoin will have a large volume of transactions or not having a volume at all, what he means is in two ways 1 it means the level of adoption of bitcoin in the larger society and second, Satoshi statement shows how decentralized and unpredictable bitcoin is even to Satoshi himself that is why he could not make a stands statement on what bitcoin will be in the next 20 years.

In the year 2029, bitcoin could have a 21 million transaction volume or have zero volume.

Of course I expect the volume to be very large due to the increased demand for Bitcoin and the increase in transactions on the network tremendously. I think that what Satoshi predicted of a very large increase in volume after 20 years happened only 10 years later, the global adoption of Bitcoin has increased at a tremendous speed, especially In the past two years, although the increase in the block size of Bitcoin causes an annoying problem for everyone because it leads to delays in transactions, but on the other hand, this is good news because it means the expansion of the spread of Bitcoin.

Hopefully someone holding a crystal ball will answer your question OP. While at this time we do not have the special ability to see the future of bitcoin whether it is still trading above $10K, $20K, $30K or $100K. One thing for sure is that as long as there is interest in bitcoin, we will still see it as something of value. I feel this thread fits better on a speculation board.

As a human, it's not possible to forecast about future which is 8 years away from us. But if Bitcoin exists until 2029 the no doubt the transaction volume will be higher than today. It's the same like you mentioned in the thread, I don't know your quote source, either "no volume or high transaction volume". But I believe we have overcomes no volume zone. At least in 2029 wouldn't happen with no volume IMO. But at the end of the day, it's a cryptocurrency and anything would happen at any time. So any judgments wouldn't consider accurate today.

If we're just the same by that time with the situation right now, then it's no longer a question because we know what's happening.

It's still a long way to go and there will be some bans that will disrupt the market and as well as adoptions being declared by some countries too. We'll never know.

He wasn’t sure as to what would be the outcome, so he knew between the two things one was bound to happen , it might be the increase in future or that no one cares. But right now we already know that it is the increase in transactions, because we are already seeing that now.So in future it is going to get bigger, although I am still wondering what it would be like when all the bitcoins are mined.

We have seen how the whales (both individuals and institutions) are buying up billions of dollars worth of bitcoins and storing them away. And some of have always feared that in future that there might not be any coins left, although I don’t really believe that, because I feel the price will always increase to fit in with demand and moreover none of these people will hold it forever. If price and transactions fees should get high in future, it might affect it.

It isn't hard to see why he said that.

Initial iterations of Bitcoin were not meant to scale, even though the limit for block size was 32MB at the very start. Probably would've been bottlenecked by the bandwidth of the nodes at that time, and wouldn't be able to scale too. It was refined to a more reasonable 1MB thereafter.

Satoshi's prediction lies on the premise that better solution to scale will eventually be implemented and the computer hardware continually gets better. Bitcoin would then be a more viable currency and offers intrinsic values that the payment systems doesn't offer at that time. People would be more compelled to use Bitcoin rather than the other payment processors. That, or a superior replacement comes about or a catastrophic event destroys Bitcoin.