Cannot figure out where this tag is coming from

For some reason, this “Red Category” tag automatically appends to all my emails from this particular account. I’ve checked all local and account tags and it does not exist. There is only one rule attached to this account and that is the one to append the green label.
Does anyone have any insight how I can remove it?
Screenshot 2023-09-20 at 9.41.00 AM

thanks for your help!

It is not an eM Client tag. It looks like a Microsoft tag, say from

So it could be added by the server (configured in webmail), or maybe by another application connecting to the same account. Those would be the places to start looking.