I used Nextcloud for both files and my PortableApps for years but it always had a hard time managing all those tens of thousands of small files. Lots of sync overhead. So I found Seafile and couldn’t be happier. I don’t just have my PortableApps in there now, I sync my Windows Documents, Pictures, Videos and Downloads folders. Seafile is very good at tracking partial changes in files so it doesn’t always need to sync an entire file when just part of it changed.

Also: It’s just a file sync service without any auxiliary features.

Basically the only answer that takes the question seriously and brings facts to the table instead of an opinion.

My solution is basically what @mojolobo mentions with Nextcloud behind it and I love the concept. Because Obsidian (via a WebDAV plugin on the phone) just syncs with the “Notes” folder in my Nextcloud root it really is just a bunch of .md (markdown) files. It gives me an added sense of security (on top of the self-hosting aspect) because I can see those files everywhere I have Nextcloud installed, I can edit them manually if I wanted to. On the PC you just point the Obsidian app to the folder, on phones you do it via a WebDAV plugin.