I’m on mobile when I tried but there was no search option. I will make a proper reply (edit this comment) once I get back to PC. I tried both suggestions in this thread, not possible to rename “basic”.
The Basic that can be changed in settings starts with capital B. I tried it also but it’s not the same and the lower case basic.
Update: I was able to delete all the messages i found in “basic” inbox etc and then the next day the poof! …“basic” is gone. Coincidence or that was the fix?