Unfortunately Err01 is a generic error that tells you nothing about what's wrong. Some command sent to the lens isn't getting a valid response.

I would be surprised if the use of the extension tube had anything to do with it. After all, the lenses are designed to have metal contacts dragged across them, shorting contacts, etc. on a daily basis. They have to be designed to cope with any amount of play in the contacts.

The reason you aren't able to focus is that STM lenses are typically focus-by-wire, i.e. the lens's electronics are adjusting the focus based on electronically sensing the position of the focus ring. If the electronics are misbehaving for any reason, that won't work.

The fact that the focus and aperture are both down, as opposed to just one, suggests maybe the lens's control board is dead.

That said, the pre-STM 18-55 lenses were prone to the ribbon cable between the control board and the aperture tearing. It's possible that Canon never fixed that design problem, and that the electronics just won't do anything if they can't control the aperture. It's hard to say.

When you zoom the lens in and out, do you hear a dragging? If so, it's probably a torn ribbon cable. If not, the electronics are probably shot. But without tearing apart the lens, it's anybody's guess.

Either way, I'd probably suggest taking this as an opportunity to trade out the kit lens for something more robust, like the 15-85 (or even its predecessor, the 17-85, which you can find for maybe twice the cost of replacing your kit lens with the same model).