Here's a quick and simple Level 20 build, ignoring magic items, outside spells, shapechanging, and flying speeds: (I don't have time to research shapechange forms, items, etc.)
Wood Elf: 35
Monk 6: +15
Wizard 5 (Bladesinger): +10 when Bladesong is active
Rogue 9 (Scout): +10 and Cunning Action...