I noticed that Airbnb has removed the blocking feature, this time completely, it seems.
When I started hosting, there was an easy "block" button, that only asked you once if you are sure you wanted to block. Then recently, it became a "report" feature where you go through some reasons for reporting, and then asked you if you "also want to block" at the last pop-up. Now, I realized even this is gone.
I saw @Lisa723 has posted that we can block guests by reporting as "They're being offensive" -> "They're being abusive or hostile" from Google Chrome, but this is no longer working (I tested with all different reasons in case as well).
I have just submitted feedback to Airbnb to bring back the blocking feature and explained how it matters for hosts' safety and wellbeing to be able to be free from terrible guests communicating, harrassing, or booking with us again. I hope you can also do this and give them your feedback!