If you have a phone with T-Mobile spyware then it almost certainly also has a locked bootloader with no official unlock method. What are you expecting people developing alternate OSes to do about that?

The obvious way to get a phone not running T-Mobile spyware is to not buy a phone from T-Mobile.

Not trying to be snarky here, I have one of these phones too. Though if you happen to have a T-Mobile Oneplus phone like I do it is possible to flash the international ROM and replace the T-Mobile spyware with Chinese spyware.