Hi, this has been a massive ingoing issue in Teams for Mac for an eternity.....i started this thread months ago because of the exact same issue and all i get in response from MS is to be patient and they are working on a fix.....put simply, Teams wont share
screens for things like excel but only some powerpoint, which is really annoying....something happened when we all upgraded macOS.
the only workaround i have found to date is to only choose ‘desktop’ as your shared screen and open the file you want to share on your desktop whilst closing all others.....quite annoying, even worse if you have automatic alerts on some programs installed
as when you share your document, others can see your alerts coming in!.....good luck... but in short, until MS fix this, thats the omly solution!