Construction for the non-nuclear parts started a while ago and is proceeding.

https://www.world-nuclear-news.org/articles/terrapower-break...

The non-nuclear bit is the key there. Site construction is not the challenge. Turning a theoretical reactor design into a working reactor design is.

As far as I can tell, in its 20 years of existence, TerraPower has not built a reactor. nor had one of its designs built by someone else.