Yeah, but can you post events anonymous there? I tried it a couple of Years ago and i didnt See that Option. But maybe that changed since then.

Also it seems Less active for my country (germany). In my area there is a instance called https://bonn.jetzt/ which is quite active and is also posting on Mastodon.

There are some Sites which do this thing: https://alternativeto.net/software/rebrickable/ .

But sadly they all are properitary and all of them Seem to cost a few dollars for alternative building instructions.