Invoice not uploaded by supplier on gstr1 but tax paid in 3b

If you have proof that the supplier has paid the tax in his GSTR-3B, then credit should have been availed before September 2020. The condition for claiming credit is that tax has to be paid to the government. There is no condition that the invoice should be uploaded in GSTR-1.

Credit cannot be availed now as its time barred.

Credit was availed by me in July 2019 only when I got the invoice 

can my supplier upload now so that I don't have to reverse it ?

Yes. This can be done.