Is GST R 9 optinal

Yes, GSTR 9 is optional, provided the gross turnover during the financial year 2017-18 is below Rs 2cr.

If gross turnover is below 2cr, can we file GSTR9 after 31.01.2020. Hope no late fee or penalty be charged.
Please advise

No......... As per Notification 47/2019 CT , it's optional for taxpayer whose turnover is below 2crore & said return shall be deemed to be furnished on the due date if it has not been furnished before the due date. Means after due date you cannot file , it deemed to be filed & final on the basis of GSTR 1 & 3B filed for the said period