Of it's a general issue with the players forgetting rule, talk to them about switching systems. I wouldn't play Pathfinder 1e for example with a very casual or rp focused group. There are so many systems that do exactly what we want on different levels of crunch. If you need recommendations you can ask in this group, but talk to your players. This works especially when your players don't care about the system you play.

Other than that, there are a ton of cheat sheets for how mechanics work online, to print out.

Hope I could kinda help

Depends on the casualness of the group.

Pick-up games, almost nobody knows the rules. Don't use complex games with them, use tiny little indie games instead. Get an OSR game like Knave, and it's almost impossible to not understand the game.

Longer-term groups, I do expect everyone to read the rules, and using more complex games is fine. Someone who won't, and especially if they picked a more complex class or skills, needs to read the book, change characters, or go to another group.