In finding creative ways to open multiple vaults on the same computer, one easy solution could be to create a read-only bind mount and then open the vault for viewing-only. However, when trying to open a vault in such a read-only filesystem, obsidian currently refuses.
Allow obsidian to open a read-only vault that cannot modify anything, but allows for browsing.
Could use an overlay filesystem with e.g. /tmp as the writable folder, but you might accidentally make a change thinking this is the writable vault.
Could use other approaches like nested vaults or syncing the same vault between two folders on the same computer.
This would be the ultimate solution: Option for pop-out windows to have panes as main window like file explorer and outline