This game's anti cheat measure is so annoying...
I tried various things with the modded apk version, so far probably only useful in Abyss mode which is still helpful because farming Abyss is going to be a chore real fast (and you must do it for progression)
What you do in Abyss is:
-use x100 damage to stomp all enemies and first boss
-leave the place right before you fight second boss but choose suspend instead of retire (choose the right button)
-set your damage to x1, reenter Abyss and fight second boss normally
-you can finish the run without getting 10021 error
Hope anyone can figure out how to avoid 10021 error in story/farming stage/towers