Many people are wondering about compatibility of FabFilter plug-ins with the next version of macOS, Big Sur. As far as we know it's not yet certain when Big Sur will be officially released. It's likely that the current version of our plug-ins will work right away but we'll only know for sure once it the release is official. We'll then test with this release and update this forum topic with our findings.
In any case, we always recommend to wait with updating to new major macOS releases on production systems until it has been out for a few weeks at least.