One caveat is that downgrading the apiserver is not guaranteed to be possible, since the schema of some types in the API may have been migrated to newer version

One caveat is that downgrading the apiserver is not guaranteed to be possible, since the schema of some types in the API may have been migrated to newer versions in the etcd database that the previous version may not be able to read. There are tools such as Velero (https://velero.io https://velero.io) which can restore a previous snapshot, but you will likely incur downtime and lose any changes since the snapshot.