I turned on my Mac one day and found that Alt + 3 no longer types a hash (#) symbol, but types a pound (£) instead.
I’ve checked the keyboard input source in System Preferences and it’s set to U.S. (which is to be expected). I’ve also found I can type a hash symbol with Shift + 3, but this is undesirable as I’m a website developer, use hashes frequently, and it’s in my muscle memory to hit Alt + 3 for a hash.
What would affect this?