https://9to5google.com/2023/01/12/google-pixel-t-mobile-upda...
unlocked, carrier-agnostic phones are the way to go.
My daughter's Pixel 5a update, for example, was delayed but it was purchased from Google.
To be clear, the update _does_ come directly from Google but the device won't show that the update is available until the carrier gives the green light. The factory image can still be sideloaded.
The P7P is the first phone that I've not purchased outright, and that's because TMO was willing to give me a ridiculously generous offer to trade in a OnePlus 7t.
edit: another link -- https://www.androidpolice.com/pixel-t-mobile-update-delayed/
With the Pixel updates, at least, the updates come through Google but the carrier (at least TMO) can prevent this from happening even if the phone is unrestricted.
You can also just update the phone using the OTA Google provides on a page and ADB to side load it.