Annotations disappear or are invisible depending on which device I host from

[wilpercy]

If I start a Meeting from the iMac and share a document all other members can see my annotations and add their own and the record of these edits remains. 

If I host a Meeting from my iPad or iPhone and share a document I can annotate from that device and the marks remain. I can annotate from either of the other devices and the edits remain on the host's document but disappear after 5 seconds on the screen of the device making the annotation. 

Collaboration is impossible. I've checked Meeting settings on the Web portal and annotations are enabled for everyone. 
I'd really appreciate some fast help on this. I fly to Britain tomorrow. My wife will have the iMac in Japan. We plan to hold ZOOM classes for students and sorting this out would make sharing the work much easier. 
Thank you.

[wilpercy]

Thank you for taking the time to reply. The use of Zoo's Whiteboard is one solution but what I really want to do is share material I've already prepared, for example Bingo cards and other picture/text based worksheets. It is more interesting for students to participate by marking those documents, but I suppose my wife will be able to share stuff and we can all annotate them. It's just that it's a heavy load for her since I usually do everything from the iMac.
I don't follow your comment about sharing a portion of a screen on an iOS device. The only options I see on the iPhone are Screen/Photos/iCloud Drive/Dropbox/OneDrive etc. Sharing a screen results in people seeing the whole of my screen and I don't know how to limit their view.
Thanks for any further thoughts.
Incidentally, why is the option to share from iCloud Drive omitted from the menu when sharing from the iMac (see attachment) but included in the iPhone share menu? Seems inconsistent/unhelpful.