I tried syncthing with Obsidian and kept getting collisions and conflicts. So I ended up paying for a year of their Sync. It’s been flawless. But now that I know a bit more about selfhosting, I will try again with this scenario. $8/mo is too much.
You could sync it with NC in sort of a janky way. Using Rclone to connect to NC via Webdav. Then rclone mount that remote and put your vault in it. Or maybe just symlink it? I’m not sure if Rclone can do a persistent mount that would stick through reboots though.