If Microsoft Teams online in Safari isn't working, it might be because of Safari's cross-site tracking prevention. To fix this follow these steps:
In Safari... Go to the Safari menu, then Preferences. In the Preferences window click the Privacy tab. Uncheck the "Prevent cross-site tracking" checkbox.
Note: You might want to re-check this checkbox for once you're finished using Teams in Safari, if you want to maintain that protection option.
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