Linux

For phone, a couple things.

Look for Mobile Device Management. I've been meaning to do this for family for years.

Flyve is an open source MDM. I've only tested it so far. You may want to look around for others.

To help with file management on Android, I setup sync jobs between the phone and a desktop (or a user's laptop) for certain folders, things like DCIM, Download, Movies, Pictures, etc (and certain app data folders such as Camscanner) using Syncthing-Fork on the phone, and Syncthing or SyncTrayzor on a pc. Doing this enables file management from the pc, as changes can sync back to the phone (and since I want my photos on my pc anyway...). Syncthing can work across most any network, including the internet and your phone data plan (so don't let it sync big stuff using data). It can be locked with a password too, to prevent little hands from mucking things up.

You could, in theory, just let it sync the entire sdcard, but lots of stuff changes all the time, such as app data in the Android folder. No reason to sync that stuff. Plus doing that doesn't permit finer control of sync for things like DCIM, which I permit to sync over any network and any power state.

Syncthing also works between two or more phones, or PCs (windows or Linux), and has lots of flexibility for sync. I use it extensively to share stuff with friends so we don't have to think about sharing, especially for larger files. I sync files between phones with no PC, some sync jobs use a pc as intermediary so both phones don't need to be connected all the time, etc.

Another sync tool, Resilio, is really good. But on the phone it's a major memory and battery hog, so I use it only for it's selective Sync feature, and keep it turned off otherwise.

These are just my ideas, everyone's use-case is different. Your problem is one I've been lazily working on for years, so I look forward to the other ideas that come up here.