Is that what is happening!
I've been experiencing this with SublimeText and VSCode!
I've taken screenshots, and a video, but had not submitted any bug reports yet.
Whenever I make a new file, say 'foo.html.haml' the system will append .h to the file.
I'd guessed it was a system wide issue, and uninstalled the new XCode just on the off chance, but that made no difference.
Maybe Apple should have held back the Sequoia release like they often do!
Edit:
These sorts of ridiculous issues are not doing anything to stop me considering moving my dev environment to Linux full time :-/