Downgrading from macOS Monterey to Catalina

The Time Machine backups made under Monterey are different than Catalina's Time Machine backups, and since the structure has changed, Catalina does not know how to read the Monterey backup.

If you have an older backup done under Catalina, you can use Migration Assistant to migrate your Catalina files back from that to your new Catalina installation. It needs to be a clean erase and install type installation for this to work.

PicklesDominic wrote:

Is the file structure similar enough on Big Sur that it would work?

It's not that it has to be "similar enough," it has to be identical. I believe it changed between Big Sur and Monterey also, so I expect that won't work either. Usually one can only restore or migrate from the same MacOS, but almost never from a newer one. I don't think macOS Big Sur runs any faster than Monterey, in fact I would expect Monterey to be more efficient.

PicklesDominic wrote:

Is the file structure similar enough on Big Sur that it would work?

It's not that it has to be "similar enough," it has to be identical. I believe it changed between Big Sur and Monterey also, so I expect that won't work either. Usually one can only restore or migrate from the same MacOS, or from an earlier one, but almost never from a newer one. I don't think macOS Big Sur runs any faster than Monterey, in fact I would expect Monterey to be more efficient.