Build 1809 has not had the best track record for Windows in the past two months: the October update brought in issue after issue and, though this current issue is not, allegedly, directly related to it, Windows just seems to have a hard time keeping bugs at bay.
The latest problem seems to be the way Windows associates files with their default programs: some users find themselves unable to set Win32 program defaults for various apps, for example, and file type combinations by using the “Open with” command or even Settings > Apps > Default apps.
One Reddit user has come up with a temporary fix that might work around it, but there’s no guarantee it will work for everyone:
This might help: OpenWith_direct_context_menu.reg
Don’t know about 1803, but on 1809 it sort-of works.
1st step: select program (might need to click More programs) and click OK (important!)
2nd step: select program again. This time the always use this app checkbox should appear.
Check it, and click OK (important!)
Repeat a few times if it still does not work.
There is another advantage to this replacement – it forces the OpenWith option to be visible if somehow Windows disables it.
Meanwhile, Microsoft has added the issue to its support page and promises to fix it in a week’s time. No rush, guys.