Shift-Scroll and Ctrl-Scroll not working on Ubuntu

Hi, I'm running WebStorm on Ubuntu 21.04 and horizontal scrolling through Shift-Scroll does not work for me. Instead, it just opens up the command popup window that usually appears by pressing Shift-Shift (don't know the precise name). The same thing happens with Ctrl-Scroll (brings up the "Run Anything" popup).

Manually assigning a keybinding for horizontal scrolling does not work, as the mouse shortcut window does not detect the Shift/Ctrl modifiers.

Edit: Other (keyboard) shortcuts that rely on Shift/Ctrl are working. Also, horizontal scrolling works in other applications without issues (e.g., Sublime Text).

Would appreciate some help :)