With Android 12, anyone can make an app store. Previously you had to let the user approve a bunch of prompts for every install or update, but the new API allows silent background updates just like on manufacturer apps.
Of course you need explicit permission from the user to install apps (that just makes common sense) but I've been using F-Droid Basic which works like a treat.
Only Amazon has tried to launch an alternative app store so far, and I'm it sure if they use the new API that makes automatic updates possible. However, there's nothing standing in anyone's way to bring competition to this market.
If you can come up with a better store, you can take one of the many open source app stores out there and add a sales feature to turn it into a business venture and take on Google and Samsung. I'm not sure how this will go down on iOS when they will eventually allow installing external apps, but I imagine the situation may be quite similar.