For what it's worth, I just fired up my two portal gen 2 in the closet, updated them and the adb setting just worked. The adb UI is a little jank and doesn't appear to enable but it does actually work. Got them set up as Home Assistant dashboards

I'm a Meta employee so who knows if I'm in some magic gatekeeper but ADB definitely didn't work on these even as an employee before

I’m very interested to see if this develops until a full bootloader unlock. Picked up CIB hardware on eBay for $70. A general purpose Linux kiosk for this price is a no brainer.