This time I will share a little opinion with the OP about the most profitable investment in the future. in several reviews you discuss the money involved in real estate and the money spent on building an apartment can be returned by investment, when the money spent on building an apartment is what is called property investment which is very appropriate if you want your money back, one way is to sell the apartment it can also be profitable quickly. I have several ways, if you have an apartment, rent it out for the long term and sell some of it so that you can get 50% of the money back.
I can try investment that can hold my capital down even though I don't get a cash flow but I will not invest in something that will tie down my capital and also require some maintenance service cost in the future, it might be profitable in the long run but my current financial goal can't handle such investments and that's what I see in this real estate thing. If you build and you don't sell on time and decide to rent out, you will be making money but their will be cost of maintenance.
Bitcoin for instance is a capital intensive investment, not cash flow and it's better but if you have enough, you can still turn it to cash flow if you stake it or use it as loan but as I said you have to be smart about it if you decide to try something of this nature. If you don't have the money to go high in real estate and you don't have another source of income after the establishment, you will be frustrated later in the future but it's more profitable for long term.