As i recommended to parent, buy a synology. It does everything both of you are talking about. If you're only trying to sync between computers, just use CIFS - \\192.168.0.5\sharename\ - in windows right click "this PC" on the left in an explorer window and "Map Network Drive". For cellphones, there's "DS" apps for all the features that the webUI exposes - File browser, audio player, surveillance (NVR is built in, or was), video system similar to plex/netflix but called DS video. and that's all "out of the box" - there's several dozen "addons" that are click-to-install.

and look, i am sure qnap and Aghyzzicgh from aliexpress might do this too, but i can't speak to them. I bought a synology on recommendation from a friend. My first one got hit by lightning (yes) and i had to buy a new NAS but the drives still work. i've replaced the original drives, but they still work. i installed one in my kid's machine to hold games. My current synology is a 4-bay dualcore with 2GB of ram.

it works perfectly for all this stuff. my phone automatically backs up photos to it when i connect to wifi, for example. If you put your syno on a public IP, you can hotlink to content on it. there may be ACL shenanigans, i have no idea. I don't use it that way.

why don't i use my synology that way?

Because i run a public nextcloud instance to be able to synchronize my photos and documents and hotlink them.

derp https://nextcloud.projectftm.com/index.php/s/synoscreenshot