You are opening the csv file in binary mode, it should be 'w'
import csv
# open csv file in write mode with utf-8 encoding
with open('output.csv','w',encoding='utf-8',newline='')as w:
fieldnames = ["SNo", "States", "Dist", "Population"]
writer = csv.DictWriter(w, fieldnames=fieldnames)
# write list of dicts
writer.writerows(list_of_dicts) #writerow(dict) if write one row at time