[I must confess I sniggered when I heard this name. It sounds like a deliberately invented rationalism squared joke… also known as QBism (of course). Not sure about the science myself but / and it feels very cybernetic to me… there are ‘many worlds’ they are just the worlds each of us live in. And with a major antecedent turns out to be Frank Ramsey, therefore a link to Wittgenstein, no wonder! Also there’s a claim that ‘the first quantum Bayesian was von Neumann – truly there were only about 30 people in the 1950s.]

https://en.wikipedia.org/wiki/Quantum_Bayesianism

Quantum Bayesianism – Wikipedia

See also

https://www.quantamagazine.org/quantum-bayesianism-explained-by-its-founder-20150604/