Cayo Perico Heist is the most profitable way do make money in GTA V right now. I alone im able to make as much as 1.5 million in one hour with this heist.
I suggest you to do this heist since you can do it alone. To be able to do it you just need the submarine Kosatka.
I started playing GTA Online the same time this heist came out and I did not have eneough money to buy the submarine, but I got a shiton of free stuff (like apartament, SecuroServ Officer and such), so I just farmed a bit, buyed an warehouse and started doing the importation jobs (Car theft) from SecuroServe Officer until I got eneough money to buy Kosatka.
If you don't have enough money to buy Kosatka, you can use Cheat Engine you get youself 5 million and buy Kosatkka and helicopter that comes inside it, its is really useful. This little money is safe to get with cheating.