then why do you support this thing at all?

I don't? I've said multiple times that I don't.

Can somebody tell me what's the minimum guaranteed attention span in people reading stuff online so I can crunch down any points that aren't a binary of "Down with this sort of thing/Up with this sort of thing" to not have people waste my time by knee-jerk assuming my stance without reading what I'm saying? Maybe we need AI summarization more than people say we do.

Also, this is me doing that for Google now. Best I can tell Google isn't stopping sideloading, they are stopping sideloading of unsigned apps in devices with Android security certifications.

The second caveat is irrelevant, in that uncertified devices presumably don't get Google services and the Play Store, so outside off-brand Android retro handhelds it doesn't matter. The first caveat is important, because on paper you can still install stuff from a website or F-Droid or the Samsung store or whatever but those developers will have to leave their info on record.

What you need to do

Complete these two steps:

Verify your identity: Provide information and documentation to confirm your identity as an individual or an organization. Register your package names: Prove ownership of your apps and register them with your verified identity.

This isn't the full app certification you need to publish on Play Store, as far as I can tell. In their words

Android developer verification is a new requirement designed to link real-world entities (individuals and organizations) with their Android applications.

This is very bad for a number of reasons. Just not the reasons people are reporting.