@yagirltrose Hello, So you've been a guest user with your gmail account at the student org. in France and now want to connect to another school tenant in the US with the same account?
First, did the org. in France remove your account properly from their tenant? Do I understand it correctly that you've tried to leave the org? https://docs.microsoft.com/en-us/azure/active-directory/external-identities/leave-the-organization As you can see that can only be done if the account isn't disabled, if it is you need to contact their admins.
But from what I can tell regarding the info it seems as if your Teams account is trying to access the org. in France but cannot do it as it has been deleted. And to be able to connect to the new org. in US you need a new invitation from them so you can be added guest user in their tenant and sign in to the new org.
Try using a InPrivate browser window (incognito) when dealing with this as no information is being cached. It could be a good idea to wipe the Teams desktop cache to reset the app as well.
On Windows: Type %appdata%\Microsoft\Teams (via Start and hit enter) and delete all content in that folder.
On Mac: ~/Library/Application Support/Microsoft/Teams
Good luck!
