Manual requests intentionally bypass that, as their own documentation states when you enable that setting. Plus "check for updates when I press a button" is enormously different than "automatically download and install updates in the background". Wanting one without the other is entirely reasonable and technically simple.

Even if it wasn't, it's unreasonable to offer a "check for updates" button that just turns into an indefinite progress bar forever without mentioning "can't check on this network" or something.

Also, as I mentioned, it does work sometimes, which is why it's clear when it's breaking. Though I didn't mention it earlier, it remains broken even when I turn off the metered mode, so yea. I'm pretty sure the updater is just plain broken most of the time.