Anyone resolve emails disappearing on i13 mini?

My mother was using her phone to look at emails and suddenly they started disappearing. She asked me to check. Everything was gone back to 2017. I thought she might have accidentally "Select All" and "Delete" but they weren't in her deleted folder.

When I went to her laptop that she hasn't used in months the Outlook 16 synced the emails into her deleted folder. I copied them to her Inbox. Suddenly many of her emails appeared on her phone, but not all. Several thousand were in her deleted folder. I Selected them and moved them back to her Inbox.

Next thing she tells me all the emails I recovered are gone again. All in the span of an hour.

What the heck? I haven't seen one solution on here. I much prefer POP3. OST's and iPhone are driving me crazy.