DDB only supports official 5e material, if WotC ever releases a 5e beyond 20th level book then we would likely get access to go beyond 20th level on DDB, but until that day happens we can't (using a single character sheet).
Yeah, it's important to note that any level past 20 is pure homebrew modifications to the core rules system and so not supported by DDB. DDB allows homebrew within the rules of D&D, but not homebrew modifying those rules themselves.
The only official support for D&D 5E is in the form of gaining an Epic Boon for every 30,000 xp you gain beyond 20th level (355,000 xp). I have seen talk in the DEV videos that they will be adding Epic Boons, Blessings, and Charms to DnDBeyond some time. I believe they are on the Timeline.