Problem with preview on device at dreamweaver

Per the link you give in the original post...

"Effective from November 16, 2021, the functionality to preview pages across multiple devices has been discontinued across all Dreamweaver versions. We encourage you to explore the Real-time preview feature to preview the pages on multiple browsers."

The QR code generator has been disabled by Adobe. They now expect you to use a non-replacement called Real Time Preview, which for a large number of users, never actually worked correctly. 

For testing across multiple devices on the same network, a local testing server works great. Once your site is set up in the server root folder, you simply turn on the local server (right click and run as admin, even if you have an admin user account), then browse to your your computer's local network IP address followed by the site's root folder, for example: 123.45.6.78/MyNewSite, on any device connected to the same network to preview your work.

I use XAMPP it's free and very easy to use.

depending on how comfortable you are with the code, look at Node.

Ben posted some time ago an embedded tool, I guess that is also a great alternative.

The main idea is to simply save your file (html, php, js, css, json... whatever) and see the result directly displayed on the target device

I don't use Device Preview.  I upload work to my server and test it.  Or I use a local testing server.