The other Quicken file needs to have a distinct file identifier so that we may delete the cloud account associated with the original Quicken file. For example, you may create a new Quicken file (select File > New Quicken File...) without any accounts and enable sync in preferences so you may view and delete the cloud account associated with the original Quicken file.
This is necessary because when we open or restore an another version of the Quicken file with the same file identifier, Quicken is not resetting the cloud account appropriately at this time. I hope they will let us know when they have addressed this issue but, for now, before opening another Quicken file that has the same file identifier embedded, delete the cloud account.
Note: Only File > New Quicken File... generates a distinct file identifier. All other forms of creating a Quicken file, copy the embedded identifier from another file.
Restoring a backup has certainly become complicated.