Err 01 and no manual focus (Canon lens)

my Canon EF-S 18-55mm f/3.5-5.6 IS STM just stopped communicating with my DSLR (Canon EOS 77D). Furthermore, I can’t even use manual focus anymore.

Right before this happened, I tested some extension tubes for macro photography. One of those extension tubes did have some wiggle room and did not click in-place correctly. I then got the following error message when taking a photo with this particular extension tube:

Err 01
Communications between the camera and lens is faulty. Clean the lens contacts.

Since this moment, my lens isn’t communicating with my DSLR anymore. Maybe it’s just a coincidence as correlation doesn’t imply causation.

What I’ve tried / discovered so far:

  • I’ve tested another lens on my DSLR (working) and my lens on another DSLR (not working) => The lens is broken, not the DSLR. Phew.
  • When testing the lens-camera-combinations, I noticed that my lens produces a super-high-pitched and barely audible electrostatic noise while the other lens (Canon EF-S 55-250mm f/4-5.6 IS STM) does not.
  • I suspected that the extension tubes’ connectors damaged my lens’ connectors. When examining the lens’ connectors, I did not find any damage though as they seem perfectly fine and the extension tubes’ connectors contract as expected when pressed on.
  • Next, I cleaned the lens’ contacts with cleaning alcohol on a cotton swab and also wiped them with a microfiber cloth.
  • The aperture is displayed as F00 (immutable) and my camera is unable to use autofocus with this particular lens.
  • I then covered the large connector (also tested covering both of the non-elevated connectors) with a piece of tape in order to test whether I’d be able to shoot with manual focus and fixed aperture. With this workaround, I was able to take a picture without getting Err 01.
  • But, I was unable to focus, even manually (switched to MF on my lens).

What else could I try? What might be broken and how could I fix that?

I’m not a fan of taking the lens apart if potentially unnecessary, but — assuming I know what I’m looking for — I’d be willing to do that.

Lens' connectors with tape over largest connector.
Aperture displayed as 00.
Extension tubes.
Extension tube's pins.