@PeterJones said in File type associations not working:
it’s at the mercy of the OS as to whether the OS will propagate such settings to the user, or completely bypass them
It worked reasonably for me. I ran my installed Notepad++ v8.9.1 As Administrator, then went to the File Association setting, picked customize, typed .pcj (which is a file extension that didn’t have any associated app or filetype), then clicked -> to move it to the Registered extensions column. If I then exit Notepad++ (to get out of Admin mode), and double-click on blah.pcj in Windows Explorer, it opened it in Notepad++. (And looking at the registry, I can confirm it added HKCR\.pcj to point to Notepad++_file, and HKCR\Notepad++_file sets the shell\open\command as expected. (But maybe you didn’t think it “worked” at this point, because it doesn’t necessarily change the text of the “file type” column in Explorer. Even if it doesn’t, the double-click did what I expected.)
When I tried with the preferences dialog misc > .nfo, it edited the existing HJCR\.nfo to point to Notepad++_file (with a Notepad++_backup entry pointing to the original MSInfoFile. When i double-click on an NFO file, Windows actually pops up a Select an App to open this .nfo file, which includes the “Notepad++ (New)” entry (because Windows has been trained to not fully allow applications to hijack extensions, because users hate it when an app does that without their permission) – and from there, you can choose whether you really want to.
But by doing it through the Windows OS Open With interface to begin with, you make sure Windows knows it’s you who wants the change, not the app, and so lets you do it more easily there.
IOW: it works for me on Windows 11 as Notepad++ tries it, with the caveats that Windows 11 is trying to protect me from nefarious apps, so might require a confirmation; and when I do things the way Windows OS wants, it works as expected rather than having to do the extra steps.