I use syncthing to sync my notes between my PC and Laptop. It works pretty well.

GitHub: https://dev.to/padiazg/how-to-sync-your-obsidian-vault-using...

For my work notes, which are not allowed to be stored outside company resources, I have set up a git repo and use a plugin that auto commits.

It does not work well for sharing to a mobile env but works great for desktop.

If you’re on Apple devices only, then iCloud sync is free and works on all devices.

I no longer use Obsidian, so not sure what’s the best option for e.g. Linux <-> iOS sync except their service.

I'm quite fond of the obsidian-gut plugin and syncing to a private Forgejo instance.