Command + Shift + 5 and Command + Shift + 6 are the selected keybinds for StructuredDiscussions on macOS (on Chrome). However, these two keybinds are already mapped to macOS's operating system built-in screenshot functionality. Therefore, you can't use Cmd + Shift + 5 and Cmd + Shift + 6 to induce strikethrough/computer code formatting if you're using a Mac.
Perhaps it would be better to emulate what Google Docs has done and change the strikethrough keybind to Cmd + Shift + X, and maybe for computer code, Cmd + Shift + C?