I’ve been a DM for many years, and in all that time I’ve had maybe three players read the PHB. I don’t mind explaining the rules, but it would be nice to not have to remind the wizard how spell slots work (again). Is this a common thing for most groups?
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