I believe that the video was misinformed or your recollection is a bit fuzzy. The closest true approximation I can muster is "there is no commercial molten salt reactor design yet approved by the NRC, and the NRC approval process may need updates to consider reactor designs that significantly deviate from the common water-moderated types."

I believe it's less outlawed and more not really approved for use due to insufficient research.

The process for licensing a LWR is well established. Commercial LMFBR (Fermi 1) and HTGR (Peach Bottom 1) reactors have been approved in the US but those were a very long time ago. Anybody who wants to license a new reactor type is going to work through an extensive process with the NRC to determine how exactly it is done.

They built an MSR in Wuwei, China and just got approval to start it.

https://www.world-nuclear-news.org/Articles/Chinese-molten-s...

AFAICT materials research is a big part of it. At 800°C even water is pretty reactive; the salt is much more so. Even though an MSR does not need the high pressure of water-based reactors, you can't make all the piping from graphite or platinum.

LFTR?

Liquid Fluoride Thorium Reactor but I believe this reactor is using uranium[1].

[1] https://www.nrc.gov/docs/ML2024/ML20241A071.pdf

LFTR is just a trade name from a guy named Kirk who tried to rebrand the Thorium fueled Molten Salt Reactor.

So basically yes but like all thorium reactors it has to start with enriched uranium first.

Yes, they are illegal to build.