User assigned managed identity cannot approve pull-request on behalf of team

Question

I have created a user-assigned managed identity and added it to azure Devops.
I want to use it as a bot for automatically approving pull-requests.

Question 1: I cannot add it as a reviewer for pull-requests. Is there a reason for this?

To circumvent Question 1 I tried to set the team, which the managed identity is a member of, as approver.
But when I try to approve the pull-requests using the user-assigned managed identity I get this error:

Failed to set vote: Invalid argument value.Parameter name: TF401186: You cannot record a vote for someone else (user fca4f388-714e-422a-8a95-c0766390e272).

Question 2: How can I use the managed identity for approving on behalf of the team? Or is it simply not possible?