Forced phasing for new content, and locking it behind walls or completing questlines is a huge oversight on blizzard. The new 9.2.5 content completely removes old undercity capability (specifically world event achievments) from any shadowlands toons unless they party sync or complete the prerequisites.
I’m not seeing anything new on my 60 that hasn’t touched Calia’s questline. Tirisfal still defaults to the BfA version and Zidormi is still hanging out to swap to the old version.