And to clarify, it's not "blocked", rather it hasn't launched in EU countries (and indeed reported to be due to worries regarding legal compliance, but afaik no official statements on what aspects of (presumably mostly GDPR) law Threads has / might have issues with that FB/Instagram don't, nor whether there's significant work to be done or if it's just that their legal team haven't yet finished deciding that it can launch there.
oh, indeed! For me it was showing just a Threads logo when I had "enhanced tracking protection" enabled in Firefox. After disabling it, I can read the website fine. Thanks!