Onedrive

[king1]

Several hours of study and battle later, I'm not much closer to solving this.

From what I can see both phone and PC are registered through same email and Microsoft account.

Have gone over this numerous times on both devices. There's no apparent place to disconnect the 2.8gb email attachments but system reports it as 57% of the 5gb allocation.

Mr Google points to a Microsoft thing called Microsoft Power Automate. The facility to have Onedrive backup Outlook attachments is there amongst many other options.
This was not activated in my case but I decided to turn it on and turn it off. Nothing changed with the 2.8gb problem.

Am I asking for trouble if I uninstall Onedrive, do a deep clean with Ccleaner, reboot and reinstall?

Thanks
Microsoft Power Automate

not sure there would be any point, it sound like it is working as expected... 

have you tried logging into https://onedrive.com website? 

In there you can see your files - bottom left shows storage used/allocated, it's clickable for more info, which also provides a link to Outlook attachments