

The only privacy-focused service is self-hostable, libre, open source and, often, free. Investing in a local server and running something like a SMB or CIFS sync to a hard drive you own is the best next step. Servers aren’t expensive, either. You can use a £100 potato or reclaim an unwanted PC. The only factors you should spare no expense in are the drives and their storage. Next important is power supply. Well-known Asia-based brands only.
Once you’ve got hardware, the software is fairly simple. I use Linux running Samba on my local network with Foldersync on Android devices occasionally uploading, but there’s also Syncthing (which I haven’t tried), Nextcloud (which has a database system that can be a pain, but is one of the nicest and complete cloud programs and has apps for everything*) and more.
Did you mean: diarrhoea