Just got the tmobile android 12 update on my Oneplus 9pro global version and its causing issues

WiFi Calling for T-Mobile on Android 12, regardless of whether you use the Global/NA, EU, or T-Mobile firmware, does not work.  A number of devices, including Pixels are experiencing the same issues with WiFi Calling with Android 12.  It is one of the many Android 12 issues that are going to be a problem well into the Android 13 release cycle.  

If you need WiFi Calling, like I do or just want your device to remain on a reliable firmware.  Use the MSM Tool for your device to roll it back.  This isn't an easy process but excellent walk-throughs can be found on the XDA-Developers forums for this.  Once you roll back, which will completely wipe your device, so back it up if you value anything on it.  Enable Developer Options and turn off Automatically Install System Updates.  You will still get the annoying prompt for the update, which you can force close the system update app to get rid of until you reboot your device.