You can see the EU a little bit like a microservice mesh standard; once your microservice is integrated, data flows, resource sharing, statistics/observability, and so on become easier in various ways, although you may have to adapt to common standards.

In legal and practical terms, the UK is still currently strongly compatible with the EU, despite Brexit. Another way to look at the situation: the UK is currently in an early fork stage of the codebase, and remains more-or-less compatible.

The biggest opportunity from Brexit -- which, strangely, may not only be available to the UK, but also to keen observers within the EU -- is the chance to introduce some local code changes without all the usual code review stages and interface negotiations.

Will everything that the UK does as a result create improvements? No: plenty of these attempted changes will fail -- some badly -- and hopefully we'll all learn from those mistakes. But there will certainly also be policy and procedural changes that result in unquestionable improvements that are re-usable elsewhere.

(disclaimer/context: I believe that Brexit was a mistake in economic and political terms, but that the UK could eventually rejoin the EU if-and/or-when the upsides are clearer to people, and that it's an opportunity to learn)