Last ones
18d. Managed to continue in Burma's capital(7). R???O?N
20a. Scruffy, a French cartoonist(6). ???I??
16d. In New York must wear a suit no matter what(2,3,4) I? A?? ???E
21d. Ancient city, favourite with artist(5). P???A
24a. A red alert worried one who has a gallery, maybe(3,6). ??? ?E?L?R