The thing with these apps is, not your suggestion in particular, is its not ever as it was 20 years ago "use this app it does this", now it is, "use this app it will maybe ask to ship your data to NSA or China, ask for account registering signup, for sure it will make some network calls to who knows where and include adtracking and other nastiness, and will nag about some license or buy-up".

Termux, ssh and rsync. Thats it. It works. I tell my phone, try to rsync when its been charging for at least 5 minutes and its evening time. Hurray.

The other thing is that these apps invariably screw usability up in some way. I use Sweech as a Wifi file server on the phone, but to get pictures off... whoops, no multi select. so if I want to grab the newest 50 photos off the wife's phone, that's 50 checkmarks to click (I'm not geeky enough to have Termux on the wife's phone). Or apps that only talk to a companion app on your (Windows or Mac) computer using a proprietary protocol. Or simply need a crapload of taps to get the job done.

Whereas the rsync method is exactly this: "syncphone" on my main machine. If it doesn't connect, nudge the phone so it wakes up (it'll connect anyway eventually; the phone seems to wake up on its own now and then). And then it's all automatic and scriptable from that point. I realize that perhaps 0.1% of smartphone users have the skills to automate things at that level and therefore care.

The auto rsync when charging is a good idea. I guess Termux can still get access to the battery/charge state?

Another example of user hostility: While on Android phones, at least older ones, bulk transfer of files via USB to/from a Linux machine has always been hit and miss, it's been rock solid on iDevices. Just do "idevicepair" and after that, transfer away to your heart's content, fast and solid. Only now I read that the latest version of IOS may have messed that up too, in the name of security of course.