You can't make laws for every single possible future reality. We need courts that uphold laws even when billionaires try to dodge them using shady techniques. The problem is that big tech often gets away with murder because they can afford expensive lawyers. Especially in the US laws are essentially meaningless for the rich. This is not so much the case in Europe.
I have heard some positive signals from the European Court of Justice that they are taking the challenge from big tech seriously and that they are going the extra miles to understand these issues. If you're particularly interested, many judges talk about this in the Borderlines podcast series by Berkley law. But it gets really dry really fast haha.
I don't believe in signing authorities. It's not effective - Google can't even keep malware off the play store - and it's an authoritarian move. Hell, most apps in the play store spy on their users, profiling usage to sell to advertisers along with ID codes that makes it possible to combine data between apps and build detailed profiles of individuals. The problem is not apps that are not signed - the problem is the whole economy of apps that work as Google intend them to.
Also, it's a basic question of rights. It's my phone, I bought the hardware, I own it, I install whatever the fuck I want on it.
Everything takes a long time, but things are happening. If you search for the terms "fine apple EU" or "fine apple EU" in your search engine of choice you'll see there's quite a lot going on.
I have some personal friends who are working with this stuff for the European Commission. It basically takes a long time to build a case against tech giants, and then once the Commission fines them these fines will be appealed in the EU court system, which will take even more years to process.
It's annoying that there's not a magic switch to flick to make Google and Apple comply with EU law, but that's the world we live in. If the EU just banned Google and/or Apple it would probably backlash tremendously (never mind that I doubt they have the authority to do so even if they wanted), so they have to move a bit slowly. :)