For the record: I believe that a flow page move CAN happen but only with the right to create a flow page.. I'll check in with the team and perhaps stewards should grant that to themselves for the purposes of renames etc where that's an issue.
Yes, you have to be able to create a Flow board at the destination. That means either the destination is a Flow namespace (there are none for user talk on public wikis) or you have to be able to create a Flow board anywhere.
It's still not clear whether they tried to just disable it at BetaFeatures (that may be possible even if it wasn't enabled as a Beta Feature, since we have a script that populates that preference).
I've filed the steward part as T126229: flow-create-board for bureaucrats?, global renamers? stewards (done) (and "Global rename script" ?).