None of the desk clips I was looking for would work! So I decided to go try and make my own. This is the result for my 20mm thick desk. Made it for my ikea desk (GALANT series). I'm sure there are many other similar designs on thingiverse but I couldn't find them.

Please post in the comments if you want it for a different sized desk! Also let me know if you want thicker walls/different sized cable hole, etc. (I wish I knew how to use the customizer for this!)

Uploading pictures of it soon.