This happens every new Android version with OnePlus. OnePlus releases them usually a few months behind the end of initially release cycle getting all the older phones onto the newer build. Covid has been making this worse, plus people left the team when Oppo and OnePlus merged teams. Kinda wish they would just stop doing it, but this is why phones maybe shouldn't ship with a working OS anyways and make the user suppl…
I think this goes against the main reason people buy phones from mainstream brands. The reason is the features and ecosystem that come with such devices.
If you are a tinkerer or prefer to install your custom OS, then you'd choose a "foss" device like the pinephone, librem or other.
If you buy a device for convenience, with the expectation that it just works, you buy an iPhone.
If you are somewhat in the middle of that spectrum, you consider an Android device where you trade some convenience with the ability to intervene more deeply with how the device works.