Additional meeting and call-related features and issues within Microsoft Teams for Education
This didn't work for me.
The thing that helped the most was this post https://github.com/L-C-P/TouchPortalTeamsPlugin/issues/1#issuecomment-1603856454
along with googling "can't switch out of developer mode"
Once I'd disabled the previews on the Teams Admin site, waited a day or so, then relaunched teams, all was well again. looks like the preview or developer modes have got a disabled API (potentially to avoid undetermined exploits) - though it would have been INCREDIBLY helpful if Microsoft had actually mentioned this somewhere (ya know, like in the API enable/disable dialog!!!)
In any case mine is working after managing to revert out of all preview/developer mode features. Happy Days