Another x-callback option on Mac :
If you don’t want to use full markdown syntax , bracket the x-callback link between less-than < and greater-than > this makes the link visible and active in Obsidian.
example: <x-devonthink-item://lotsofletters>
It also appears to work with, some but may not be all, application-specific link-calls, application examples such as: agenda://, ithoughts://, omnifocus:///