Another here who came to a bit of a stop in the SE corner. 21d a new word for me but solved once I got the clever 24ac.
Yes I thought the “modern” before theatre was just an extra bit of help, with it being 20th century if that’s not spoilerific. Probably my COD that.
Overall I thought this was one of the best Everymans of recent months, some of the surfaces are excellent.