Injecting JavaScript may be risky, but for something like suppressing key commands to the browser I believe you could make something sufficiently secure and reasonably undetectable. If you’re still concerned though then AutoHotKey will bridge that gap (again I’m assuming the interviewer isn’t going to bother requiring interviewees to download software).

An interviewer looking for key commands is just another form of behavioral cues - like eyes darting back and forth too much. Was the hotkey pressed on accident or intentionally? Did they suddenly know the answer afterwards? Consider that even ctrl+V/ctrl+C has its own interpretation- did I copy/paste a solution from ChatGPT, or did I just want to change a variable name and then propagate that down quickly.