Can't Socket Supports Into Cast on Freeze

The only support I can socket into Cast on Freeze is Impetus. I can socket in triggered skills but no supports for them. This seems wrong as a billion people are socketing Spell Echo or Inspiration next to Comet in Cast on Freeze set up.

I had the same thing on PC using controller, but if I switched to mouse I could slot Inspiration/Spell echo etc.

I play on PC using an xbox controller. Although I get an error message, I'm able to socket support gems. However, I'm not able to socket a skill gem (for instance, socketing cold snap or comet into cast on freeze). That said, I can do it with mouse and keyboard, but couldn't find a way to do it using the controller.