RPGMemes

To give you another rec, which is often named as an intro to PbtA systems for dnd players: Dungeon World. It still borrows quite a few things from DnD (which are imo the worst parts of DW).

And as the other user wrote, reading other system can even be helpful just to steal stuff for your DnD group. PbtA (or one based on it) is one that imo every GM should've played, because it teaches so many important principles that are relevant in any systems you play - but in PbtA they are far more explicit (and well explained in the rulebooks).