Potential workaround: Right-click your tenant icon within the Remote Desktop app, then click Settings, turn off the default settings slider, then in the resulting side panel turn off "Fit session to window". This has worked for many of our users, but not all.
We have multiple users running into the same issue. Remote Desktop will not use only the right-side monitors without using the left-most monitor(s). If your monitors, going left to right, are identified as 1,2,3, then you can use 1+2, or all monitors, or any single monitor. But you cannot have Remote Desktop use only 2+3. (With 4 monitors -- and presumably more -- it will use the correct quantity of multiple monitors but only starting from the left side.) Reverting to the previous version fixes the issue, until it auto-updates the next time the app is closed.
I haven't tried this yet, but there is a registry key that MS says can keep it from auto-updating:
https://learn.microsoft.com/en-us/azure/virtual-desktop/users/client-features-windows#admin-management
I'm not keen on pushing out a registry change to all affected computers, but it seems likely to come to that unless a new version is released soon. And it appears that all computers are affected, but those who don't try to have the left-most screen exempted from Remote Desktop don't notice it.