I think one of the more interesting things about this is not the fact that Iran claimed it possesses ICBM capability - that is something Iranians and outside observers have known for a while now. No, what's interesting is that Iran is saying this in the first place. https://twitter.com/fab_hinz/status/1326802936601702401

Let's make it clear - Iran probably doesn't have an operational ICBM. But it has all the components of the dormant Project Gha'em; a solid fuel """SLV""" program started by Shahid Moghaddam. Iran could probably put together an ICBM very quickly via that program.

This is likely the message, and it's aimed at the incoming Biden administration. Biden has talked about returning to, and then extending the provisions of, the JCPOA. Iran is pretty much saying; we can be to you what North Korea was to Trump.

That is, a country that changes from not being able to strike the US mainland to one that can, inside 1 presidential term. That coupled with the recent news that Iran is 12 times over the JCPOA uranium limit lends Iran some nice leverage. https://www.bbc.co.uk/news/world-middle-east-54912402

The goal is to block any US efforts to try to put additional restrictions on Iran's nuclear program beyond the JCPOA, by building up enough leverage to make such an aspiration too politically costly.

The manner of it is a bit odd though. In @fab_hinz's thread you can see the original clip of IRGC Gen. Mousavi has been censored to hide the bit where he said ICBM. But it was proclaimed by the TV presenter in another clip. Maybe not everyone is on board with this proclamation.