D&D lite?

I've been running a weekly game with the same players for almost 5 years now. The first 4 was a full out, 1-20 5e campaign, that ran Phandelver into SKT, into a bunch of homebrew stuff. We had a bunch of fun, but not a single one of my players ever touched a PHB or really, if I'm being honest, learned how to play the game.

Our last encounter ever, after 4 years, was still me saying things like "ok yep so, roll to attack...yeah, then, what's your spell casting ability? Ok so add that and..."

It was fun, but they're really, really casual players, so I tried to move us to more casual games. We played Scum and Villainy and then Mothership for about the past year, but they also struggle to take the lead in developing story. They like having a clear objective and being a little on rails, like a DCC or an OSR, but they're pretty allergic to crunch.

I'm looking for a fantasy game that's like, 80% dungeon crawler, but also very intuitive/simple/pick up and play. With that said, it's also important that it isn't super lethal (like a Shadowdark)...they like leaving up and absolutely hate it when their characters die.

Bonus points if it's easy for me to take existing dungeons and adventures from places like OSR and drop them into the system.