His new form of theatre might include a set design wherein all the doors and windows have bars on them, as the protagonist, who is not imprisoned but feels as though he or she is, journeys through a series of loosely connected incidents and meets characters named man or clerk.

Expressionism

Explanation: In simple words, expressionism refers to the form of art whether in respect painting or drama etc in which the artist tries to convey an emotional experience rather than expressing the perceptions of the external words.

In the given drama, the protagonist is not in jail but still fells that he is and also meets several other characters to convey an emotional message with a subjective perception.

Hence the given case depicts expressionism form of theater.

sounds good to me mate!