https://startplaying.games/join-game/intro-to-monster-of-the...
https://startplaying.games/join-game/thieves-in-the-night-16...
Or Cypher System https://startplaying.games/join-game/black-rain-ripples-[cyp...
Both are pretty fun systems!
The Cypher System is probably closer to D&D, but the combat / rules / stats are a lot more streamlined, so in my experience it's easier to jump between narrative and action.
Monster of the Week is a bigger (and welcome!) departure from the traditional TTRPG formula, and is probably closer to what GP was looking for -- it's a very light "game" system on top of the players building a story together with the DM.