Not fines, but the potential for litigation brought by end users with potential for unpredictable damages. This is what creates fear in companies and forces them to change their behaviour to avoid.
Other industries have to contend with the threat of such lawsuits. Big tech is mostly free from such threats.
This is not "my" solution. This is "a" solution. You only want specifics so you can shoot it down.
If online advertising was regulated, e.g., prohibited, then it would take away some of the incentive for Facebook and Google to profit from data collected from/on users. We already saw this "no advertising" rule in effect when commercial use of the early internet was prohibited. AFAIK it was not backed by any legislation. We saw the Google founders release their work as an academic project vowing to combat internet advertising. We saw the Facebook founders disagreeing over whether to show ads. We can see how things played out. The temptation of onlne ads was just too great. Now they are beholden to Wall Street to keep up the surveillance and keep selling ads.
This time around, we could permit commercial transactions, including "e-commerce", but we could prohibit the use of the internet to advertise with violations giving way to not just fines, but potential for lawsuits from end users against advertisers and anyone selling online ads or online ad services.
I have never heard any argument that claimed that what Facebook does is valuable only if they are allowed to use the data they collect in any way they choose. If Facebook was simply a service to allow users to have a page on the Facebook website, and the company was not allowed to conduct surveillance and give third parties (e.g., advertisers) access to those users, I think users would still find Facebook valuable.
If users would not pay for such a service, then the problem is Facebook's, not users'. This is why "Facebook will always be free." It must be free. Otherwise users would find other free solutions.
I believe were Facebook to begin charging fees, we would still find ways to use the web to share photos/video and exchange messages with each other, through a website, for free. Facebook could prove me wrong by charging fees to all their users and letting us see what happens. They will not do that. They are afraid to test their monetary worth to end users.
It is the same story with Google, their search engine and all the works they acquired from third parties, which users often believe Google developed in-house. Those "services" have value to users apart from being vehicles in which Google collects more data and otherwise strengthens their online ad services business.
The aim of this legislation would be to force companies wishing to do business on the internet to sell, for money, something of value to users (cf. third parties) instead of simply operating as middlemen conducting surveillance for the benefit of third parties. No more "user is the product".
Now let's hear about your solution. After all, you stated "Everyone wants things to change" and that must include you.