Just under 21,000 so about what you'd expect for this game. Considering the pandemic, people not wanting to go back to football, broken habit, less disposable income etc then it is hardly a surprising crowd. In the promotion season under Warnock this fixture had a crowd of 21,018 which is a difference of 127 people.

21/22 - 20,891
19/20 - 23,846 (helped by high season ticket sales following relegation)
17/18 - 21,018 (promotion season)
16/17 - 22,776 (Friday night + Warnock's arrival)
15/16 - 15,287