Interesting. I wrote the article a long time ago, but I still use the approach it describes to this day. I have this setup on Ubuntu MATE 18.04 without issue, r

Interesting. I wrote the article a long time ago, but I still use the approach it describes to this day. I have this setup on Ubuntu MATE 18.04 without issue, running MATE 1.20.1. When you say super key, do you mean the windows key? And hitting it opens up the main MATE menu? For me, it opens up as expected: https://i.imgur.com/dZzQt1t.png https://i.imgur.com/dZzQt1t.png and choosing an item from it does the expected thing. For the i3 mod key I use alt. Is it possible you have both MATE and i3 set to the same super/mod key?