I understand that "stocks in play" (boomer slang for meme stocks) display whacky irrational behavior that makes no sense, or there is just a temporary combination of high volatility at relatively low market cap, and therein lies potential profit opportunities. It's not clear whether an algorithmic trading strategy is applicable to such situations although I do see people always mention "stock screeners" which seems to just be code to filter time series.

After taking into account transaction costs, slippage and taxes, it's not clear that there is anything better to do than buy and hold low-cost index funds.

Also, there is a separate problem around having the computer structure/segment large trades to reduce market impact to get the best deal possible by looking at the order book to wait for people willing to buy/sell a lot at reasonable prices or something -- that is a different kind of algorithmic trading from what most people mean when they say they are backtesting a trading strategy like moving average crossover or something.

It all just feels too much like alchemy. But, if you become independently wealthy by writing code or you just don't lose a lot of money and you find it fun so it's sort of like paying to do something you enjoy, God bless.