It's about Reagent, not re-frame. And the former does work with 18 but with some caveats, e.g. https://github.com/reagent-project/reagent/issues/579 There's also a port of re-frame that uses a different, more light-weight, React wrapper: https://github.com/ferdinand-beyer/refx. But I haven't used it myself so can't comment on it at all.

ive used refx and the API is largely compatible with re-frame unless you use things like dynv in a subscription

the biggest issue ive ran into was the lack of good debugging tools like re-frame-10x, and more importantly, if you use materialized views (i.e. subscriptions returning hiccup), then you'll need to refactor that code to not return hiccup, or use a custom defnc macro that interprets hiccup, but that becomes awkward real fast