Some of my customers insist on Teams meetings and they have been problematic. I have the same flicker issue when sharing Excel. Thanks to those who suggested work arounds! But, "don't use that feature"
is not a true solution. Microsoft needs to fix this or everyone will continue to run to other solutions.
Try do disable Hardware Acceleration under Options - Advanced in Excel.
I think this problem is related to the hardware acceleration not being well managed by Teams. In our Company I disable that (disabling in all Office application) in every PC I configure for some problems we had time some time ago.
We had this problem with Teams when sharing an AutoCAD window, but not for other application (or at least not yet).
So I think that hardware accelerated application are not well managed by Teams when shared.
Also I think that the Desktop isn't "hardware accelerated" or managed in a different way, so the problem isn't showing when sharing the whole desktop.