Found these courses via freeCodeCamp -

I analyzed these 100 now-free Coursera courses using Class Central's dataset. And I discovered that 85 of the courses offered certificates that you would normally have to pay for. The other 15 courses were already free but didn’t offer a certificate.

None of these 85 courses belong to a Coursera Specialization. And Coursera is only keeping them free until the end of May 2020. Once you checkout, you will have 180 days to earn a certificate.