Solved! I had the same problem: everything worked alright (zoom, meet, etc), except for Teams. The virtual camera was detected, apparently no problem at all, but other participants could not see my video. Alternatively, I was using the teams web client in Chrome, but the quality was not very good. Using combined information from other posts in this forum, and experimenting, I have solved the problem this way:
1- Quit OBS and teams completely.
2- Uninstall OBS (export your scenes before if needed), remove its application support directory (/Library/Application Support/obs-studio), and the virtual camera plugin (/Library/CoreMediaIO/Plug-Ins/DAL/obs-mac-virtualcam.plugin). Don't worry: the new installation will restore them both.
3- Install OBS version 26.1 (NOT 26.1.1 nor 26.1.2). Looks like something in those versions caused the problems with teams. Here you have the link:
https://github.com/obsproject/obs-studio/releases/download/26.1.0/obs-mac-26.1.dmg .
3- Run it, and the wizard will come up. I chose use for virtual camera.
4- Start virtual camera (remember now it is on the right side panel, not in the tools menu). Your password will be required because the plugin will be placed in the DAL directory again).
5- Run Teams. Ta-da!! Virtual camera up and running again! :)