Apparently the OSI approved the Unlicense as a "Special Purpose" license a few months ago, but I do not see what the special purpose is anywhere on their main site. There's some more background in this mailing list post:

https://lists.opensource.org/pipermail/license-review_lists.opensource.org/2020-June/004890.html

I'm still not clear what the "special purpose" is that they're suggesting, though. Seems like they don't want to be seen recommending it because it's somewhat weirdly drafted and is partially a public domain dedication.