Well, you have the Obsidian URI scheme, where you can use a link like obsidian://open?vault=ObsidianNotes&file=TestNote
But Notion does not support that x-callback-url scheme. And if you use a link that links to another app, it just won’t work. It can only do http:// links.
But there is a thread here where someone figured out a workaround. It’s a bit of a hassle. And it might only work on iOS using the shortcut scheme. So this might not be relevant to you. But it might spark some ideas of how you could find a workaround. Using URL Scheme Links in Notion | Kevin Jalbert
But I don’t think the obvious way of using obsidian:// URIs would work, sadly. I’d suggest making the feature-request to Notion to natively support x-callback-urls. That would be amazing if they did!