You can now launch the XPAND Code Reader from the App Clips Code.
This is only for iOS 14.3 and above, but you can try to read it from the standard camera.
XPAND/QR/EAN/UPC code reader will be launched without app installation.

Zooming by pinching is also supported.
In some situations, the reading distance of XPAND Code has been increased several times.

For iOS 14 to 14.2, you can still launch directly from the QR code without installation.
For Android (excluding some models), you can launch it directly from “Try Now”, though via Google Play.

Both the App Clips Code and the QR code have an embedded URL for launching the app, but accessing the same URL in Safari does not seem to launch the App Clips.
So far the only way to launch it from the web page is via smart banner.

Also, App Clips does not launch with any QR code reader other than the standard camera.
This seems to be a specification for the standard camera app only.