There also seems to be a plan to add uefi support to u-boot[1]. Many of these kinds of boards have u-boot implementations, so could then boot uefi kernel.

However many of these ARM chips have their own sub-architecture in the Linux source tree, I'm not sure that it's possible today to build a single image with them all built in and choose the subarchitecture at runtime. Theoretically it could be done, of course, but who has the incentive to do that work?

(I seem to remember Linus complaining about this situation to the Arm maintainer, maybe 10-20 years ago)

[1] https://docs.u-boot.org/en/v2021.04/uefi/uefi.html

Per TFA, the Orange Pi 6 Plus ships with UEFI, but the SoC requires a vendor specific kernel.

The orange pi 6 plus supports UEFI from the get go.