I have a daily todo note that I keep in the top right pane so its always visible. I have two vaults and would like this note to exist in both and keep both in sync.
I tried using a symlink in Linux and placing it in the 2nd vault but the file was not recognized as an .MD file.
Have you tried “hard links” rather than “symbolic links”?
Symbolic links have the extension .symlink, visible in the file properties.
It’s not actually a .md and Obsidain doesn’t recognize it.
However, hard links keep the file extension.
In Osidian, the changes are not synchronous (snapshots): if you modify the contents of the file in a side application, you must save it to see the modifications of the file update in the open window of the Obsidian. Or update the file yourself. (Tested on Win10).