The Atom editor is based on Electron and it does not behave in that way on Mac. At this moment I have Atom running under two logged-in accounts on that same machine.
Is Obsidian doing something with Electron that causes this?
Followup:
As a test I tried another Electron application, Left (https://hundredrabbits.itch.io/left) which is open source. Like Atom it does not block multiple users from opening the app simultaneously. Clearly this is an Obsidian problem, not an Electron problem. Can we classify this post as a bug report?
To block simultaneous access by different users some shared resource must be locked. This would normally be either a file or a port. I’ve checked using lsof and thus far I can’t find the culprit. Is Obsidian making use of some port or some file that is not specific to the user?