Thank you to those who responded. I've just found this on the London Stadium site on their news page about the Muse gig:
General admission tickets bought through London Stadium give you a choice of view. They include access to the pitch standing area, as well as the option to take a seat in our unreserved lower tier seating. London Stadium also has reserved seated tickets. Pricing and locations of these tickets will be confirmed in advance of the on-sale. Booking limits will also be confirmed in due course.
