HI @JimmyYang-MSFT ,
Thanks for your answers and your help.
I was not able to join any meeting as external users (I tried with different external organisation). I had the same issue with the browser (chrome) or the desktop client.
I was able to connect to my Teams account.
I finally found a solution: I remove the cache/cookies of the browser. I didn't test yet but I have probably to do the same thing with the desktop client.
I don't know exactly where the root issue come from but probably a conflict between azure and microsoft365:
Anyway the issue is solve for me now.
Thanks for your support,
It has been a while, how is everything going?
If you have any update about this issue, please feel free to post back.