So it turns out what the 6th mouse button is doing out-of-the-box is sending the win+tab keyboard inputs to the computer, so I had to remap win+tab to what I actually wanted (which was win+shift+s to trigger screen grab). Annoying that it works out like that because now win+tab on my keyboard also takes a screenshot, but also it’s probably better anyway because win+tab sucks compared to alt+tab and win+tab is easier to hit than win+shift+s.