An update for those still receiving the mandatory Firmware Update pop-up with no ability to access the Thermostat without updating:
The 1.2.5 update is a critical fix update to 1.2.4.a2. Rather than just push the update to only those on that version (who would have received this update thru Beta) Wyze has instead decided to push the update to ALL Beta Testers who have the thermostat designated as a Beta Device in Account → App Info → Beta Program regardless of the actual version of firmware on the device.
My thermostat was on Public Release 1.2.1 (May '22) but was registered in my settings as a Beta device. That is why I was getting the mandatory update pop-up. Removing my device from the Beta Program Device List restored it to operation and stopped the popup.
As soon as it is returned to the Beta Device List, the popup continues.