

Are you saying save when you mean sync?
For easiest, if your NAS supports WebDAV that would be it.
Second is likely syncthing, but with potential sync conflicts.
For self hosting, everything past that starts getting harder involving docker or other more complex services.
I have been using Joplin with Nextcloud for years without issue on both Linux and Windows, it’s odd you couldn’t get it to work. I use Obsidian as well.