How to set a default application to open a file in mac? In a mac (10.14.6) I want to set the default application to files of type  'err' (i.e. files like test.err or output.err) to be TextEdit. 

For that I follow the description given here, and set the default application to be TextEdit.

 

However, when I double click on that exact same file in the finder, I see the following text box:



So what am I missing? Why does it nor work?
I don't know why the existing two methods are not working - they both should.

Alternatively try RCDefaultApp which as far as I'm aware still works in Catalina. [I can only test up to Mojave.]

I added this manually using the + button &amp; it actually suggested TextEdit itself. I'd suggest also checking 'Override file creator' &amp; see if that might help.