I have just tested it on a Sitefinity 5.2.3800 project and the Open a specially prepared site
option works properly on my side and redirects to the selected mobile page.
I have prepared a short video for your convenience demonstrating the behavior on my side. Since I am testing this in browser, for demonstration reasons I have set the rule to apply for large screens (the Open a specially prepared site
option could not be tested by re-sizing the browser's screen).
Can you please make sure that you have properly specified the different screen sizes in the responsive design rule? Can you please also try to modify the rule to apply for devices with large screens as shown in my video and test if you will be redirected to the mobile site when you access the page in browser?
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