Conditional statement for two conditions

I need to create a conditional to show a different header. I have seen and used conditionals before but can’t get this to work.

I want the header to be displayed for a category (let’s say category 5) archive page and the same header when single posts of that same category are displayed. I guess I don’t know how to do this and/or logic, any help is appreciated.

(off topic: years ago I had this same user name but my old password didn’t work, I am surprised I was just able to register the same user name and email again today, at some point things get/were deleted here?)