The problem is that most normal people (HN is not normal - mostly for the better) don't even understand what sideloading is - let alone actually care.
How can we fix this?
(aside from making people care - apathy enables so many political problems in the current age, but it's such a huge problem that this definitely isn't going to be the impetus to fix it)
I don't think that making "normal" people "care" about sideloading is the answer, because a) it's impossible and b) political change doesn't happen through "normal" people anyway, all political and regulatory change is driven via smaller and motivated groups of people.
The problem is fundamentally that there's a duopoly on mobile OSes that has tons of market power and if they want to dictate a change like "you can no longer install unapproved software," they can just do it.
The solution is to walk away from that duopoly, to suck it up and just stop using their products. We fortunately are able to do this (for now) on desktop and running Linux in 2025 is better than it's ever been, and more people are doing it.
To get Linux or some alternative on phones is a big task, and if you make the switch you're going to lose a lot. But most of what has no desktop equivalent is addictive social media garbage that you should get rid of anyway. The biggest thing I'm concerned about is the state of banking and OTP/2FA.
I think we need to fight for universal electronic access to the financial system as a right without a need for gatekeepers like Apple or Google. In some countries it's already the case that at many businesses you must use your phone to make payments, cash is gone, cards are dying, and you must therefore agree to Apple or Google's rules to use your phone. This is truly how freedom and democracy will die if we allow it. This is way bigger for "normal" people than technical concepts like sideloading. People on the left should inherently understand the importance to liberty of having the right as an individual to buy and sell without some megacorp's permission. For people on the right, well, remember the Bible's "Mark of the beast..."
Secondarily we need to fight for the enforcement of anti-trust laws, which half of HN doesn't seem to even know exist, or feels are in some way unfair, even though they are the cause of these problems. Government needs to reach in and rearrange markets that are dominated by one or two players, it needs to forcefully restructure those companies so that they lose their market power and can no longer force citizens to obey their will. We've done it before, such as ending company towns where you were forced to use the company's scrip at the company's shop to buy living essentials. It's worked, we need to do it again.
The problem is that I want to make calls, SMSes, use WhatsApp and Telegram, Maps and OSMAnd, NewPipe, VLC, Syncthing and a few others on the phone I carry with me.
And to make matters worse I don't want a huge, thick and heavy brick like every Linux phone I read about. I'm on a Samsung A40 now and it's not easy to find a replacement with similar size and weight.
That doesn't solve anything, though. If Google revoked your Google account and refused to open a new one, you'd be SOL - you'd either have to buy an iPhone, or move banks until you find one that gives you a physical TOTP (since many just have apps already, but those apps don't run unless downloaded from the Google or Apple stores).