This has been causing me similar problems. I see very few options in sharing /opening email attachments in iOS mail.
I have just succeeded in a fault diagnosis, though I haven’t yet found a workable fix:
I use my phone (11 Pro) to access work emails. This requires Microsoft InTune and the installation of a company management profile. I think it’s something to do with this, because I removed my device in InTune, which also removed the profile. I then performed an on/off cycle (though this may not have been necessary, I thought it a wise precaution). After this, a full list of Open with / Copy to options became available.
The contents of the management profile installed look like this:

Once these were re-installed, the equivalent screen shows only these options (with no extras available when “Edit Actions” is selected).

In summary, this looks like it is connected with the loaded profile. How to address this I can’t be sure, but perhaps the first stop is Corporate IT support (good luck with that!).