Exactly my question. I have seen a bunch of these OSs, all useless because there is no build for my phone and no described path for making one. I would love to get the T-Mobile spyware off my phone. What do i do?
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.
To clarify, some of the phones you can buy directly from T-Mobile can also be bought "unlocked" in the open market.
In general, if you want any hope of unlocking your phone (either for use on other carriers or unlocking the bootloader) then you should NOT buy from the carriers' online or brick & mortar stores.
See https://grapheneos.org/#device-support. The goal of the project is not to bring security to people's existing devices. It will have official releases with all the device-specific hardening for non-Pixel phones, but they'll be devices with solid security. They probably won't be quite on the same level as Pixels, but they'll still be ones with proper security support, verified boot support for alternate operating systems, etc.
Unfortunately all you can really do is pick up a different phone. Luckily finding an old unlocked Nexus 5 or OnePlus One on ebay is pretty easy and relatively cheap.
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.