the + ctrl on key release is needed because when button 8 is pressed, ctrl is also pressed, which meanse when you release it it is ctrl + button 8 instead of button 8, withuot it the key release wouldn’t work.
I use Easystroke - this lets me set my side buttons as I like. I set my ‘fwd’ button as an instant button to resize windows, and the ‘back’ button to move windows… saves having to hold a keyboard key and click to do the same job.