P2721Q, native support for macOS brightness keys?

TL; DR: Apple monitors (in laptops, desktops, and external) support using the F1/F2 keys for brightness control. Do Dell monitors support this functionality natively?

Context: I have a Dell P2721Q monitor attached to an M2 MacBook Pro (and an Intel MBP prior to that). I seem to recall that my brightness keys worked perfectly with it, out of the box. (Important: Perhaps this is completely incorrect; I am honestly not 100% sure, since I also use an Apple Studio Display in another setup, where it does work, and I might only be thinking of that.)

Yesterday, the monitor stopped accepting my laptop's video. After quite a long set of attempts — changing cables, rebooting the laptop, changing various monitor configurations, it still didn't work, until I finally tried the obvious thing: actually unplugging the monitor from the wall (not just turning it off by the switch). And it worked! I then got spooked and found that there was a firmware update online, which I applied, with no obvious changes. (This whole paragraph might be a red herring...)

However, after this I noticed that I couldn't change the brightness via the keyboard, or the Displays panel of “System Settings” (but see above — perhaps I never could!). I have checked that DDC/CI is enabled, and certainly all of the other settings (various power and USB settings) seem as before, but F1/F2 still don't work (I can set the brightness on the monitor itself just fine).

I am aware of and have tried MonitorControl, Lunar and other similar software (which aren't what I'm asking about), and of similar questions on places like Stack Overflow.

So:
* Was I hallucinating that it ever worked?
* If not, any idea what might have changed?
* Are there any monitors that do support this?