The no-Google-calendar-sharing-on-mobile is an absolute classic. I have personally seen multiple clumps of people huddled around a phone trying to figure out how to share a calendar with each other - fruitlessly until I butted in, because normal people don't know about desktop mode and even if they did would have no reason to think it necessary.

(If you didn't read the post, it doesn't work in the app either. It only works on "desktop.")