Okay..., you can try the following, if you want to, but,
I'm warning you, you better be comfortable messing with the Registry, back everything up, document or take screenshots of existing, better yet, export the keys you're gonna mess with!!!
You're going to perform all the following under
Computer\HKEY_CLASSES_ROOT :
Create a new key, name it notepad:
View attachment 164717
Go back to .txt and change the Default string to notepad:
View attachment 164718
Make Notepad++ your default and you should be good to go.
View attachment 164719
More caveats:
I have not witnessed any negative repercussions from these Registry writes but, use caution!
There is a possibility that if you do enable Legacy Notepad, from Optional Features, it could cause issues!