Hello Matt Bero
I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this!
Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others", I'll repost your solution.
Please click "Accept" the answer as original posters help the community find answers faster by identifying the correct answer.
Issue: Deleting Azure peering is not an option after I deleted Microsoft peering
Resolution:
Private peering took about an hour to delete after I deleted Microsoft peering. Peering needs to disable before you cancel the ER on the Partner side.
Please don’t forget to close the thread by clicking "Accept the answer" wherever the information provided helps you, as this can be beneficial to other community members.
Hope the above answer helps! Please let us know do you have any further queries.
Please do not forget to "Accept the answer” and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.