It’s a bug, it’ll be fixed in the next release (6.0.1).
In the meantime you can delete your preferences and start from scratch, which will avoid the problem (delete %APPDATA%/kicad/6.0/eeschema.json). Don’t import your v5 preferences if it prompts you – that’s where the issue stems from.
see also this thread: Cannot Open eeschema v6 (MacOS Mojave) - #14 by pseudolegolas