SUMMARY When an annotated pdf is put on google drive, and when it is opened from within google drive, no annotations are shown. In this case is it us or them the ones who aren't following a standard? ADDITIONAL INFORMATION ubuntu 18.04; okular 1.3.3 (apt-get version)
Okular does save annotations conforming to the PDF standard. The problem is very likely that Google Drive can only show annotations with an appearance stream saved into the AP dictionary. The poppler library used by Okular can't save that particular piece of data. PDF 1.7 standard marks AP as optional and expects readers (Google Drive in this case) to be able to generate them on the fly. But the new PDF 2.0 standard (released 2017) makes AP mandatory and expects composers (poppler in this case) to save them. You see, it's not easy to tell if it's us or them. It doesn't matter much anyway, we can't change others software, but we can change poppler. We quite frequently receive bugs that originate from absence of AP. IMO saving AP is one of the top missing features in poppler. If anybody is interested in helping to implement it please contact me.
I'm closing this issue because it's too broad and it's not really a bug that google drive is doing things wrong. Yes we could do things better as Tobias says, but "do things perfect" is a bug that will never be fixed since perfect is impossible to attain, so having this bug open really serves no purpose.