GTK got rid of the + in its name in 2019:
https://lwn.net/Articles/779305/
This commit replaces GTK+ with GTK in the most visible places: strings, man pages, visible svg text, comments.
Exceptions:
- All changelogs and news files are left untouched.
- Usage outside of strings/comments (code/variables, things like gtk+-2.0.pc that hasn't changed)
- Some comments that were so old that it felt weird touching them (like
requires GIMP 1.0 and GTK+ 1.0.4, that was quite a while ago)