In French, if I want to say I did it, do I use the masculine le or the feminine la?
Should I then say Je l'ai fait or Je l'ai faite?
If “I did it” means that you did something without explicitly stating what, you should use the neutral, thus the masculine
but if you achieved something, it would be more idiomatic to use
If the thing you did is explicit, then you must use its gender
Unless there's a known feminine gender behind the it, you would use the masculine