Microsoft Surface Hub 2 SmCamera - Manual (Page 373)

The most common reason you won't see the join button is if the device account’s
Exchange properties are incorrect, causing Exchange to delete the meeting join URL
from the invitation comments. This happens if the device account
Exchange property
DeleteComments is set to True . You can confirm if this is happening via the following
steps:
1. Open a web browser and navigate to teams.microsoft.com .
2. Sign in with the Surface Hub device account credentials.
3. Open the calendar and locate the Teams meeting that failed to display the join
button on the Welcome Screen calendar.
4. Select the meeting and press the expand icon.
5. Below meeting info verify if the Teams meeting join URL is present or not. If
missing, follow the PowerShell commands below to check the value of
DeleteComments.
6. If the Teams meeting URL is present, analyze the hyperlink to ensure it begins with
"https://teams.microsoft.com" and doesn't redirect to a different site. If redirected,
the Surface Hub may not understand the URL and therefore not display a join
button.
Safe Links rewritten URLs, or any other third-party link scanning service
isn't compatible with One-click join. Set up a Safe Links policy to exclude the
Surface Hub device account from this feature.
Analyze meeting invitation comments