Hi Wes2266,
Thank you for reaching out Microsoft Community. We apologize for the inconvenience this may have caused you.
You may configure the Surface Arc Bluetooth Mouse by installing the Mouse and Keyboard Center. The middle click button can be set as a 3-finger click functionality and right after installing the Mouse and Keyboard Center, please check if you can re-configure it. Kindly check this thread for instruction.
If this answers your question, please let our Community know by marking this post as an answer. Otherwise, don't hesitate to respond to this thread for further assistance.
Kind Regards,
Crest_Z