Binding of Isaac is some OG classic stuff if you haven’t played that one, and Neon Abyss is a fun side-scrolling game on a similar vibe. Rogue Legacy 1 (very OG) and 2 and Dead Cells are also side scrolling , with a dash of Metroidvania.

If you like Slay the Spire, Astrea is the same thing but with dice, and Monster Train also scratches the same itch.