It's quite nice so far, but I haven't found how to block a community from the website. The three dots menu for a community allows to block the author, the domain, the instance, but not the community itself. Am I missing something?
No, you're not missing anything - that function is not present because it was forgotten.
IMO browsing by 'All' (and then blocking communities) is a crutch for the poor community discoverability on Lemmy. If finding communities was easier then you'd subscribe to the ones you want and then you wouldn't need 'All'. I have tried make finding and subscribing easier by using Topics and including topic subscription in the onboarding process but I admit it's not a complete solution.