Hello @ade0501, I switch my S23 Ultra to the same at 10 pm with Power Saving On and Restrict App Usage set through a Routine. I don't get any notification sounds as both of those restrict additional activity by default. I don't know if the same will work on your S21.
@Fiona26, thanks that appears to have done the job. Sorry for not replying earlier but your comment didn't show on the post, only in the notifications.