Blockchain investment comes in many forms, the most common investment by which people are storing crypto for a long time before selling it out and trading it daily to make a profit.
There are other forms of mining crypto (such as Bitcoin, Litecoin, ETC, ETH ...), participating in investing in crypto derivatives (margin, future, ETF ...), working on organizing a cryptocurrency, set up a crypto project, invest in Ponzi projects and get out quickly when there is enough profit (this way has the greatest risk).
All of the above are good and everyone is doing it but if you don't want to be complicated then just buy bitcoins and keep them well, sell them when you have the right profit.

It mean invest in ponzi project is good and profitable? Tell me some ponzi scheme sites have you invested with your proof then

Useless is just a strong word as not everyone understand how the system work, how to store, secure, send and receive bitcoin but this shouldn't stop them from wanting to benefit from the industry therefore if they do have some knowledge with Investing in stock and shares, they're good to Invest. Them choosing this method over the traditional buying of the coins off exchange could be to avoid the high risk involved and thus means is more ideal and safer compared to owning the coin physically.

Still the best method of investing in the industry involving having control over your bought coins and not the specifically investing in the DeFi you speak about. Nevertheless don't restrict your options of profiting form the industry as all the methods listed by the OP can be quite profitable, you just have to know which works for you based on the amount of knowledge you have on each of the methods.

Blockchain is the process where you are storing the information or the commonly use is the transactions every time we made and by this block it will encrypt this and make a another blockchain to make it more secured.

Some of the people are using the blockchain not only in cryptocurrency also with the use into the world of businesses too

Examples
Storing of file system on schools
Storage of records and business
Payment transaction

Why go for DeFi is you can just buy Bitcoin and hodl? DeFi is risky, you might lose a lot if a big player cashes out and the price goes down. Just have a look at this exit scam with Sushi Swap, and this project looked quite serious. They're like ICOs, but not as obviously a scam because they are still new. I would not risk putting money into one of those. If the token gets released and starts trading with the price going up, one can simply buy it then and still enjoy a good profit if the project gets successful. At least, this can decrease the risk.

I haven't invested in PONZI projects for many years but my friends do and they do it very early. Of course, the returns are very high and sweet.
I will list Bitconect 2017, Minningcity at the end of 2019 until now.
I have made it clear in my post that they are dangerous and not recommended.

Stocks and ETF at present seems not to be good when you have a way to mine token through delegation and holding. Be a part of relaible startup at the Genesis stage is a great way to invest in Bitcoin. DeFi is taking on the rampage at moment so, ETF and Stocks as per crypto should remain silent.

I guess, once you do your research very well and learn what each coin represent to the people around the world who use it, you can can decide for yourself, when and where to invest in cryptocurrencies.
There are many ways you can invest in blockchain:
1) Personal research: For you to invest in blockchain stock yourself research is very important for you to know when and where to invest in the blockchain.
2) It is your choice: it's your choice to invest in any of the blockchain that sweet .

Invest in blockchain? How do you do that? You aren't investing in blockchain, you are investing in coins and tokens. What even is blockchain stocks? Those are just some normal company stocks that you have mentioned. You even suggesting people to invest in TOMOchain, a project no one has ever heard of. Their ANN thread is self moderated. Not surprised to see TomoDEX (decentralized exchange). Using hype to promote them more?
Many will fall for this hype and lose everything they invested. The number of defi projects popping up is alarming.