Just use Syncthing and whatever chat app you like.

Dont trust or use Google drive. Google wouldn't offer that space for free....they get something out of it.

Google drive is also privacy invasive, look at that guy who got banned for sending medical photos of his kid to the pediatrician. i've been using a self-hosted nextcloud instead of google drive, but these days back up to my laptop through rsync from termux over a usb cable. i've noticed with nextcloud, if I upload a folder with lots of photos, a few of them will fail and keep spamming notifications with retries. That is mostly on my old phone though.

To understand correctly: You have friends that care about moving files of their mobile by sync? Or is their only concern switching to Signal, but the lack of backup besides on the device?

Asking because:

• I have the same solution as you but the android folders - foldersync - Nextcloud variant.
• My motivation comes from privacy / sovereignty.
• My friends lack this motivation so they are happy using the cloud (iCloud or Googles) to "backup" everything.
• Any hassle by not using that needs strong motivation to endure and overcome.

So when their photos are in the cloud and their documents stay happy in mail attachments often there isn't much more to backup besides configuration. Which all those bigphone (Samsung Lenovo Apple etc) suppliers provide.

For the chat backup:

• I got my whole family to switch to Signal (at least with me and for group chats, we have them for events and topics). The leverage I used was to only use Signal for baby photos of our newborn kids which my sisters and mom just couldn't live without. 😎
• They complain about running out of local storage and not being able to bulk delete media in Signal.
• As a workaround they sort by filesize and delete a dozen big files (eg video).
• Or they leave a group, delete it along with media and join again.
• I was surprised they don't care about the files after consuming it (foto video) and happy delete them.
• After that ... the backup becomes small again.

No. Remote computers are not your hardware, your secrets always stay there.

We should all own our own hardware. Any centrally connected system is bound to fail if it is compromised. We must have modular systems, that is everyone must own their hardware.

Just do away with everything Google. You're welcome!

I self host seafile. Nextcloud and syncthing are also good options. There are people that sell hosted nextcloud and seafile

iOS has its own internal backups that can either be done by connecting your device to a Mac or a PC with iTunes for local storage or you can use a part of your iCloud storage and upload it. There is no need to add an extra layer or another provider.