Still happening to me too @ibwoo. This is just unacceptable. Don't know if anyone from Apple monitors this forum but sure hope so. How is this not a test scenario? It's a stinking text file!!! My brother word processor was more reliable. OUCH.

Here's my experience with TextEdit using Big Sur... it's CRAP!!! MacOS BigSur TextEdit Crash Issue - https://discussions.apple.com/thread/252535514