That’s a great question. As far as I’m aware, with native web technology, there’s no way to open an arbitrary Windows app.
That being said, Windows has support for registerable app protocols. So you might be able to use a hyperlink tile with something like mailto: or news: to open the relevant app if one is registered.
From my experience, app protocols aren’t used as much on Windows as they are on other platforms like Android or iOS. You might try emailing the app developer to see if they have an app protocol registered.
You can find more details on how to open Android or iOS apps here.
The following article on registering your own App Protocols on Windows might be helpful to you:
And for other people who find this via search, here are some URIs which launch several built in Windows 10 apps:
| URI Scheme | Launches |
|---|---|
| bingmaps:, ms-drive-to:, and ms-walk-to: | Maps app |
| http: | Default web browser |
| mailto: | Default email app |
| ms-call: | Call app |
| ms-chat: | Messaging app |
| ms-people: | People app |
| ms-photos: | Photos app |
| ms-settings: | Settings app |
| ms-store: | Store app |
| ms-tonepicker: | Tone picker |
| ms-yellowpage: | Nearby Numbers app |
Some of the URI schemes accept parameters. For example, you can launch the Windows Store app directly to the Squeeze Control app listing: