In a "keeping score" video about 5th Symphony by Shostakovich a director Michael Tilson Thomas says the following:
Instead of writing in the approved ultra-nationalist style, Shostakovich wrote his Fifth Symphony on the model pioneered by Beethoven; he begins his symphony with a sonata, albeit with a hesitant feel.
If I understand this correctly, sonata here refers to the sonata allegro form, first part of a classic sonata where we'd get intro, 1st/2nd theme exposition, progression, repetition of 1st/2nd theme and then a coda. Indeed, this structure kinda fits the 1st movement of the 5th by Shostakovich, with perhaps a superlong coda.
What I'm interested in though: what was this
approved ultra-nationalist style? Perhaps there are some other symphonies that provide an example of such style which apparently should differ from the classical sonata one.