That does not at all suggest that UK ISPs proactively share anything with the state.

What it means is the GDPR doesn't stop ISPs choosing to share when asked, rather than waiting for the warranted request that will come, as long as there is a lawful basis.

Again: I don't really have a problem with that. If you've ever used a website that arranges work for lone workers (freelancers who do site visits, freelance estate agents, models, dog walkers) then you'll presumably want the people who run those communities to feel able to choose to share with law enforcement when asked.