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?
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.
It’s exactly the same in Gnome.
Right click > open with (with the option of setting the selected app as the default)
See comment above from me. This doesn’t work unless you already have .desktop files and MIME types already configured for your app.