This has often been the case in the past but the situation is much improved now.

For example I have an Orange Pi 5 Plus running the totally generic aarch64 image of Home Assistant OS [0]. Zero customization was needed, it just works with mainline everything.

There's even UEFI [1].

Granted this isn't the case for all boards but Rockchip at least seems to have great upstream support.

[0]: https://github.com/home-assistant/operating-system/releases

[1]: https://github.com/edk2-porting/edk2-rk3588