The dtsi configs for the internal switch may be different. Once this is figured out you would need to submit a PR to have those changes upstream.
Aha, that's a good tip, thank you. Where would I find the current dtsi configs, and how would I compile a new blob to apply them?
I built dtc statically for aarch64 and ran it on my device with both the stock Unifi firmware, and a clean OpenWrt flash. The dumped device trees contain many interesting differences, but most importantly, we can see that the Unifi device tree advertises itself as similar to this example devicetree in the kernel source (Linking to v5.10 as that's the kernel version that OpenWrt uses). I also found the OpenWrt dts source code for v22.03.
I'm not an expert on this stuff by any means, but I'm going over the documentation, doing a three-way comparison in my head, between the OpenWrt configuration, the kernel's example mt7622-rfb1 configuration, and the Unifi configuration that I dumped. Once I figure out some interesting-looking difference, I suppose the next step is to figure out how to compile OpenWrt with these changes.