I think a lot of Brexiteers don't entirely understand
why the EU was a problem.
The only thing they saw was the EU migrant crisis and the UK not having total control over its own borders. Things I don't care about[0]. The actual problem with the EU is only tangentially related to that concern, and it's the fact that the EU is a democratically unresponsive accountability sink. When a politician wants to do something unpopular, they get the EU to do it, so they can pretend like they're powerless against it. See also: the 10,000 attempts to reintroduce Chat Control.
The easiest way to fix this would be a new EU treaty that makes the EU directly elected. But that would also mean federalizing the EU, because all the features that make the EU undemocratic are the same features that protect the EU from doing an end run around member states. The alternative would be for EU member states' voters to deliberately sacrifice their local votes in order to vote in people who promise to appoint specific people at the EU level. That's what happened in America with its Senate, and why it moved to direct election of Senators, because people were being voted in as Governor just to get Senators elected.
A lot of times we talk about political issues on a partisanship spectrum - i.e. "partisan" vs "bi-partisan" or "non-partisan" issues. The reality is that, in WEIRD[1] countries, most parties have a common goal of "keep the state thriving". The primary disagreement between them is how to go about doing such a thing and what moral lines[2] shall be crossed to do so. That's where you get shit like America's culture war. The people who live in the country and are subject to its laws are far less hospitable to the kinds of horrifying decisions politicians make on a daily basis, mainly because they'll be at the business end of them. This creates a dynamic of "anti-partisanship" where the people broadly support things that the political class broadly opposes.
For example, DMCA 1201. The people did not want this, the EFF successfully fought a prior version of it off in Congress, then Congress went to the WTO and begged them to handcuff America to it anyway. The people would like to see it reformed or repealed; that's where you get the "right-to-repair" movement. But the political class needs DMCA 1201 to be there. They need a thriving cultural industry to engage in cultural hegemony, and a technology sector that can be made to shut off the enemy's tanks. The kinds of artistic and technological megaprojects the state demands require a brutal and extractive intellectual property[3] regime in order to be economically sustainable. So IP is a bi-partisan concern, while Right-to-Repair is an anti-partisan concern.
In terms of WEIRD countries, the UK is probably one of the WEIRDest, and thus a progenitor of a lot of stupid bullshit legislation. If they had not left the EU, the Online Safety Act would have been the EU Online Safety Directive.
[0] To be clear, my opinion regarding migration is that the only valid reason to refuse entry to a country is for a specific security reason. Otherwise, we should hand out visas like candy, for the sake of freedom. Immigration restrictions are really just emigration restrictions with extra steps.
[1] Western, Educated, Industrialized, Rich, Democratic
[2] All states are fundamentally "criminals with crowns". Their economies are rapine. When they run out of shit to steal all the gangsters turn on each other and you get a failed state.
[3] In the Doctorowian sense: "any law that grants the ability to dictate the conduct of your competitors". This actually extends back far further than copyright, patent, or trademark law does. Those are the modern capitalist versions of a far older feudalist practice of the state handing out monopolies to favored lords.