Yes, it's very frustrating, that they still cannot do the client right. The client doesn't work without logging-in and I cannot login, because my private e-mail is not part of the organization which is organizing the meeting and I used the contact e-mail as my primary contact e-mail in my MS account. So the client outputs: "Someone has already set up Teams for your organization" error and that's all fun with the client. Dirty workaround is to remove my e-mail from the MS account and use there some different e-mail account. This must be a joke. My primary e-mail is my primary e-mail for good reasons, I don't understand why I should register different e-mail just because people in the MS don't understand how to write the client.
I am now using Google Chrome for attending the MS Teams meetings from Linux (rather from the sandbox). It works much better than the native MS client and it works without logging-in. Unfortunately, Chromium doesn't work for me. I don't know why, but I guess it's because MS did again something wrong.