edx-platform is now testing against both a Mongo 4.4 and Mongo 7 database. I believe it is now ready for tutor to be updated to use Mongo 7.
I took these notes when I updated my local mongo server which might be helpful reference: Mongo 4.4 to Mongo 7 Upgrade Runbook · GitHub
Since both edx-platform and cs_comment_service have been confirmed to run with mongo 7 I think there is nothing blocking tutor from updating to Mongo 7 on the nightly build. Please let me know if I can help answer any further questions.
Relevant edx-platform PR: chore: add mongo 7 to testing matrix by DanielVZ96 · Pull Request #34213 · openedx/edx-platform · GitHub