I am having this issue as well for a new MS Team connection. I cannot load the “Team” despite having the account connection set up WITHIN MS teams and connected back to Zapier. The full error message is:
We’re having trouble loading 'Team' data
An owner must install the Zapier app from the Teams store in your team to use this feature. Then reconnect your Microsoft account in Zapier.
If I go into the MS Team itself it will tell me the Zapier app/bot is installed.