I have the same issue.
All other tabs in Photos app in Catalina are there, but the photo's tab is missing. so I cannot view my photo library as a whole and not have the recently added updated features in Catalina such as all the catagorisations.
I reinstalled Catalina and checked the other user accounts to see if this is linked to my account only, but they have the same problem.
I updated my system from Mojave latest update, where everything was always working fine. I updated Catalina to it's latest version and waited for Photolibrary to do it's magic to maybe organize all pictures, but nothing ever happend....still no photos tab and still no day, week, month, year view....
My Library is on the same SSD as Catalina and stored in the regular Pictures folder.
I took a screenshot but my system language is dutch...