I have seen this asked many times but have not see a good response so I will try like others have here. Also after reading the forum here it seems very odd that this issue is well over a year old and Upwork still has not updated their procedure.
Problem is whem you to go add a microsoft cert Upwork displays the following:
Microsoft Certified Professional
As part of other changes that Microsoft is making to streamline the certification experience, the Microsoft Certification Profile feature retired on October 31, 2018.
Members of the Microsoft Certified community: you will find all your certification information - exam scores and certifications earned - on your Microsoft Certification Dashboard.
We'll have one of our team members reach out to you directly and assist you further with your concern regarding Microsoft certificates verification, thank you for your patience.
If you try to enter a certification not on the list, you’ll have the opportunity to Suggest a Certification. Occasionally updates will be made, thank you.
I would recommend adding your certification as a portfolio items until our list is expanded.
Regarding your profile, it is accepted and you can start sending proposals once you`re ready. Thank you.