So this is not a question about how to do this. I know how to do this. I also know that (at least under GNOME) it is neither easy nor intuitive. It involves manually editing several different text files to define MIME types and associating an application with that MIME type. My question is: is there an easy to use GUI tool to do this. I don’t think there is. Associating a file type to open with a specific app is easy, trivial even, to do on MacOS or Windows. Why is this seemingly simple task so hard to do in GNOME?
It is actually very easy, on Gnome you need to open nautilus(Files) then right click the corresponding file type, click "Open with..." and select what app you want it to open with and if you would like to make it the default. Which funny enough is done the same way in MacOS. You just overlooked it.
PS:This method automatically writes changes to ~/.config/mimeapps.list
PS2: Usually you can find answers to this questions in the documentation with a quick online search.
Sounds like I need to try xfce. But again - I shouldn’t need to change my desktop environment to do something fundamental that a GUI desktop environment should handle easily. No? Otherwise my desktop environment is just eye candy for xterms.
Nope. This doesn’t work when you have binaries that are not recognized by GNOME. You need to make a .desktop file for your binary first that define MIME types for that app. If it is a MIME type that is not recognized by the freedesktop.org database, you also have to create an XML file that defines your specific file type based on file extension or other characteristics. Then, you need to use Nautilus to set the default app. It’s a pain in the ass if it’s not a standard app from the Ubuntu App Store and a standard MIME type.
Unsure if it's a viable option for you, but using KDE's Dolphin file browser, it's rather straight forward for me to set default applications through GUI. Also maybe worth noting I use Mint Xfce, even though Dolphin is a QT program ported.