Hi @Lukáš Patrnčiak
Teams tag is mainly focused on the general issue of Microsoft Teams troubleshooting. According to your description, your question is related to Windows systems, which is not in our support scope.The following suggestion is just for your reference:
1.Ensure that your internet connection is stable. Sometimes login issues can occur due to network disruptions.
2.Sometimes a simple restart can resolve minor glitches. Restart your computer and try logging in again.
3.Incorrect date and time settings can cause authentication issues. Right-click on the clock in the taskbar and select Adjust date/time. Make sure the date, time, and time zone are correct.
4.Clear Cached Credentials and Restart your computer and try logging in again.
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