The Bletchley Park site, containing the not terribly interested mansion building itself, and a large museum of WWII code breaking stuff, is one charity, but on their site, in another building, is a different charity, The National Museum of Computing, TNMOC.
Historically the Bombes (electro-mechanical devices used to help break Enigma) were part of Bletchley Park's museum, but apparently earlier in 2018 they moved to TNMOC.
This is weird because Bombes are really, really not computers, unlike Colossus, which TNMOC looks after but is open to the public from the other charity's site. Colossus is one of many machines on the cusp, it's an electronic computer, but it really only does one thing and "re-programming" it involves almost taking it to pieces. But Bombes are no more computers than, say, an old-fashioned mechanical cash register is.
So this demo will be hosted by TNMOC, but the machines shown will be ones you may have seen (unless you went there this summer) at the non-TNMOC Bletchley Park WW2 crypto museum. A miniature version of this (part breaking Enigma) used to be a demo that Bletchley would do live for visitors several times a day, but TNMOC may not be offering that demo any more on their tours, I'm not sure. I assume the demo for this stream will be far more complete than the average visitor to Bletchley was interested in watching although I doubt it will have a step where people try to guess German "cribs" for the message text.
A problem for this demo, and any dramatisation of breaking Enigma, is that it doesn't feel like very much. It's loud, and the Bombes are doing stuff because they're mechanical in nature, but ultimately you can neither experience what it's like to invent this extraordinary machine, nor what it is like to be the machine while it's working, so it's emotionally a bit empty. In a movie you can suppose that breaking the code will prevent our heroes being killed by Nazis or something, but it's still a bit arms-length really.