FWIW, I used caddy on my unit, and it’s working quite well. But I’ve also had caddy running on the VPS the NAS replaced, so it wasn’t exactly a novelty.

Happy to help if there are things you’re struggling with.

I only have an iOS device, but its app is great and yes, it offers that functionality. So I reckon they wouldn’t have done this just for iOS 😄

Ha, of course “self-hosted” is the community I comment on for the first time after lurking for years, but …

UGREEN NASync. I own a DXP4800 Plus, and it fits your descriptions. Its OS is Debian (custom-built; but you can throw your own distribution on it and won’t even lose your warranty, though!), but it has a decent frontend, a mobile app even, 4 SATA3 + 2 NVMe bays, gets regular updates, is accessible via pretty much any protocol under the sun, can be backed up automatically to a lot of cloud storage providers, and I run a bunch of containers on it (which I used docker-compose for), since it ships with first-class support for it.

Overall, a huge value for its money so far (been running it for a few months), and can definitely recommend it, especially as an alternative to the incumbents like Synology or QNAP, and it’s a lot less power hungry and quieter than just getting a server rack off eBay.