> I back up files to my own cloud with a Nextcloud integration for Android.

Ouch man. Don't do that. Nextcloud is fairly unreliable.

> That being said, a monthly or so backup of devices via USB/Ethernet, like we used to in the pre-cloud area, would be enough for all intents and purposes.

And/or use FolderSync to sync to your PC, and then use a proper E2E system to back up to the cloud.