I have previously looked into this as well! This article explains the workaround I implemented. In summary: you cannot move something from a shared inbox back to an individual inbox, only shared inbox to shared inbox. The workaround is creating an empty inbox and not adding participants to it.

The workaround allowed me to move emails out of team inboxes into the Admin inbox and fully restrict the participants when needed.

This work around should be helpful, I was also looking into this. Thank you.