Try creating a custom Speed Dial with the Queue' extension number. You can add the custom speed dial from the BLF tab on the extension settings and re-provision the phone.
I ended up setting the button as a BLF manually on the phone with the call queue extension. The transfer works, and the busy status seems to be working as well.
If this doesn't cause issues down the road, it would be nice if we could just provision it in 3cx that way.