What the summary says, if you press on the highligther annotation you get "Highlight text" as a hint message, but only if "keep annotation tool active after use" action is not checked
Here too.
A possibly relevant merge request was started @ https://invent.kde.org/graphics/okular/-/merge_requests/320
Git commit 023976ccfdd79812180c85dad8ee7e3b6ac7aef9 by Albert Astals Cid. Committed on 26/11/2020 at 09:12. Pushed by aacid into branch 'release/20.12'. Show annotation tip when selecting the tool in continuous mode M +1 -1 part/annotationactionhandler.cpp M +45 -43 part/pageviewannotator.cpp M +2 -1 part/pageviewannotator.h https://invent.kde.org/graphics/okular/commit/023976ccfdd79812180c85dad8ee7e3b6ac7aef9