The message:
# pragma message “FastLED version 3.003.001”
is actually not an error message (yes, I agree – why show it when it can confuse the user?) – so you can ignore that one.
It’s just there so you can see which library version you’re using.
The message:
ld returned 1 exit status
is a linker error – for some reason linking (ld) failed.
Maybe verbose output (File -> Preferences -> check “Show verbose output during: [ ] compilation“.
Not sure if it will help.
Often this is related to the Arduino IDE – so also make sure you have the latest version of the Arduino IDE (which includes “ld”).
As for the pins used: some pins can conflict.
I’m not an expert on this, but I know some pins are so called PWM pins (like PIN 6 and PINs 3, 5, 6, and 11) – see attached pictures (which can be quite confusing).
So my advice, since I’m not an expert either: start your project with 1 button. If it works OK, add another button. Keep doing this until you see it fail. For the last PIN added select another pin.
Another approach could be using the effect that you’ve tied to PIN 12 on a PIn you know that works. Just to make sure the effect does work.