I clicked “Open launcher” and nothing happened

That button hands off to the desktop app through a creta:// link — the same trick a store page uses to open Steam. If the app is not installed, nothing is listening and the page simply stays where it is.

Work through these in order:

• Install the launcher, using the Install launcher button in the same window.
• If it is installed, start it once by hand — the handoff only works after the app has run at least once and registered itself.
• Your browser may be asking for permission to open an external application in a small bar or dialog. Allow it.

Once the app is running, the button takes you straight into it.