I had button 10 (the thumb button) bound to "xdotool key Super_L" previously on Ubuntu. Worked great, would pull up the Activities screen just like Super_L does. Since upgrading to 21.10 it won’t work. I can bind it to something like xterm, or xbindkeys_show, ‘xdotool key control+shift_q’ (which also does a xbindkeys_show), and those all work great.
If I type xdotool key ‘Super_L’ at the commmand line I can see the mouse cursor twitch, but nothing pops up.
If I try xdotool key ‘Super_L+s’ I just get an s on the command screen.
>Solution :
During the upgrade to 21.10, your account was changed to log in using Wayland instead of the traditional Xorg display server. xdotool does not work properly on Wayland. You could try ydotool, a similar tool developped to work on Wayland. While it is much more limited than xdotool and currently not anymore actively maintained, it will be able to send your key combination.
Alternatively, you can switch back to Xorg. Log out. On the Log in screen, before entering your pasword, click the cog icon and select the "Ubuntu on Xorg" session.