For Macs: I use Time Machine backups on unraid (nothing fancy but it has built in settings to support it effortlessly). There’s also https://hub.docker.com/r/mbentley/timemachine that I tried out a year ago.

I haven’t tried over vpn but as long as you can mount the share , it should be fine.

The community documentation is really good; this makes it super easy to find out how to do something or fix an issue. Adding a drive is super easy , and doesn’t require all the drives to be the same size, you can mix and match. It also supports docker on top of all of that. If you’re willing to manage all of that yourself from scratch , then I doubt you’d like it. It’s convenient for most people that don’t want to spend a lot of time managing and troubleshooting their nas.

They only stated what they do on the pc , not it being a reason why

It seems daunting, but it’s a lot of fun once you do. I started on docker desktop but moved to docker being run on Ubuntu server, but I don’t think it matter where you host it. Very easy to setup and their documentation is pretty good. You technically could be up and running in 10 minutes. Learning how it works will obviously take longer but I find that getting to actually being able to use what I want to quickly removes a lot of barrier to entry. Good luck!