I have Mathematica 11.3.0 and Wolfram CDF Player App 11.3.0 installed on my MacBook Pro running Mojave. When I create CDF files for my students I like to open them in the player app to better see what my students will see when they open them. But for some time now whenever I open a CDF file it always opens in Mathematica even if I change the file's default app in Finder's Get Info window. And CDF files do not show the CDF icon like they used to. How can I fix this?
Have you tried right clicking on the CDF file and selecting "Open with ...", CDF Player?
Yes, that works. But I should be able to double-click a CDF Player file and have it open in CDF Player because I have set CDF Player as the default application for all files with the cdf extension.
I had a quick moment to study this behavior for myself, and found that setting "Open With" and "Change All" in the "Get Info" dialog works as expected, with one caveat: if Mathematica is already running, the CDF will instead open in that. It's simply one of the launch services rules we follow since Mathematica and Player have to operate interchangeably. I.e., the behavior in response to "Whether to launch a new instance of the application, even if another instance is already running" per Apple's developer LSCConcepts documentation.
As for the icons not displaying, you might search for "reset LaunchServices" and see if that helps. If you continue to see problems with both of these issues, our tech support folks should probably get involved and gather more detail on the specifics.