Hello, these are two different file association issues:
1. I have set MC as the default for everything it supports, except for images (jpg, png etc.). I do not select image file association during MC installation (this is reflected in MC Options/File Types) and have also disabled Image support in Options/General/Features.
If I go to Windows 10 Control Panel/Programs/Default Programs/Set Default Programs and press "Set this program as default" for MC, it will register everything MC supports, including image files. This action removes my current associations for image files and as a side effect, causes MC to open them by default and fail opening them, because they are disabled in MC anyway.
It seems MC always reports to Windows that it can open all of its supported file types. My suggestion is to only report to Windows whatever the user has already selected within MC.
2. I think I've reported this again some years back. MC registers all its associations as "Media Center file". The problem with this is that within Window Explorer (and similar programs) it is impossible to sort them by type, because for Windows they are all of the same "Media Center file" type. The simple solution to this would be to add the file extension, for example "Media Center WAV file", "Media Center FLAC file" etc.