That must be some setting for you. It doesn't prompt to save on any of my several Windows machines, and I don't recall configuring that anywhere.

Strange it does prompt me to save and I also don't do any extra configuration for the Win11 Notepad. It is a fairly annoying app, and definitely worse than previous versions. But will look into what config options there are, but being a modern software I expect it's probably got limited options.

for me it only happens if I run in multiple instance mode where you can have multiple notepad++s open

I meant Windows Notepad on Win11 is doing this annoying thing, not Notepad++.