I'm limited in my 401K so I can only buy indexes, mutual funds, and ETFs. I've tried many different things and the best strategy always seems to come down to I would have made the most money by just sticking it all in the S&P500 and quit watching the market. I deviated from that for awhile and thought I was doing better because I was 5% above the S&P after 6 months and then last few months things swung the other way. I feel like people add a lot of stress to their like watching the market every day and then most of them can't even beat the S&P500 including a lot of the financial experts. I know some of you will claim you do but for every one that beats it there are a 100 that don't.
Given your restrictions, I can see why you found it hard to make any money. Indexes, mutual funds and ETFs are not going to perform much differently to the S&P500 (which is itself an index).
I have made good money on stock markets before, but only by being active, investing in undervalued companies and treating it like a part time job. I've invested in a bunch of speculative stuff, but every time I've made real money, like double/triple/quadruple my money within 2-3 years, it has always been with mid to top tier companies that were boring but undervalued. An oil refiner. A miner. A fruit cannery. A grocery retailer. Nothing fancy. Researching and doing due-diligence on these guys, then waiting for right opportunities to buy in, can take months or longer.
I've lost money too of course, but the trick with losing stocks is to establish strict rules, where you get out fast once they prove themselves to be mongrels. Bite the bullet, wear the pain, sell and limit your losses. I actually set the sell (stop-loss) orders to execute automatically if price drops too much, so I don't even have to think about it.
However, if they turn out to be greyhounds, let them run and watch for opportunities to buy in some more. If they go up a lot (past the target you set originally) then sell some to lock in profits. Now you have cash in pocket. If the price then goes down later but you still believe in the fundamentals, look for the right chance to buy back in at the cheaper price. Or look for some other opportunity.
Having said all that, I haven't been active trading for some time now. It is hard work and and time consuming. I haven't bought or sold anything since sometime well before COVID, too busy tinkering with my arcade and greenantz stuff to give it the attention it deserves (demands). All my current investments are parked in blue-chip buy-hold stocks so no need to worry about them on a daily basis.