Okay… Settings > Preferences > General > Tab Bar > Reduce did have an unexpected impact.
The tab labels actually use a smaller font with the “Reduce” option unchecked !
Tabs 02.jpg
But it’s still composed using a Bold style. I really don’t understand why, but I’ll tell you what : I could live with that ^^.
I also experimented with %AppData%\Notepad++ and Administrator mode - which was checked, indeed, because of protected files : I use that a lot. But no dice… Recreating a new folder didn’t change anything.
Thanks a lot for trying to help ! As said above, I could honestly live with tabs in Bold, now that I can at least read longer labels ^^… It’s just a weird issue.