iTunes backup is perfectly reasonable alternative to iCloud that retains e2ee, I don't know why they were dissing it. It can back up everything that iCloud can and it's automatic, you just plug your phone in, no lock in tactics.
Interacting with any device running iOS requires Apple software (or reverse engineered hacks) for many features.
However, in this case, the point is that you can use Apple software to make a local backup (and you can enforce the "local" part by doing so offline), and then use whatever you want to encrypt and stash away the resulting files.
Tresorit? Self-hosted Nextcloud?