Hi, I’m not sure if this meets all your needs or requirements.
I currently have four email accounts.
I selected the images from the gallery and attached them to a draft email, and was able to send them.
I hope that helps.
This works fine for me as described: Open gallery / Open a picture / click on share button / Select one of e-mail account. And a new mail with the pic as an attachment shows up. (Same phone, same OS version)
Have you tried the usual task like testing all mail accounts with send and receive, reboot and so on?