Fix League of Legends self cast on Mac without extra software
On Mac, the key next to the spacebar sends Command. League of Legends blocks it to prevent accidental Cmd + Q quits, so Self Cast stops working naturally. Most guides point to Karabiner-Elements. That is a maintenance burden for one game.
The fix
If your keyboard has a Mac/Windows hardware switch, flip it to Windows mode. The key next to the spacebar sends Alt instead of Command. macOS reads that as Option, which is the default Self Cast bind. Control stays in the bottom-left corner, so Ctrl + Q/W/E/R still works.
Any keyboard with a physical toggle works. I use a Keychron K2.