What are those alternatives? I can’t think of any that are ready for prime time.

Not everyone cares enough to avoid Google. Some of us that want to do so are related to them.

You can stop using all Google products.

That may be true for you, but other people face different realities. When Google implements the sideloading block it will eventually be pushed to everyone who doesn’t use a custom ROM.

The infuriating part of the Google enshittification process is that there is absolutely nothing the user can do about it.

Literally the only thing that motivates Google is profit. Controlling side-loaded apps will almost certainly boost their profits by a infinitesimal fraction of a percent, therefore it will be done. Even if consumer uproar causes Google to back down in the short term, they’ll simply implement this a few months later. Late-stage Capitalism sucks.