Clean install this morning of Catalina on my 2019 15" MacBook Pro. Store shows "No Purchases" - but yet if I go into the Music App, and look under iTunes for "purchases", they all show up.
I spent two hours on the phone with Apple (cough) support, and they even had me reinstall Catalina.
I finally, especially after finding out that my WDC MyCloud Home software wouldn't work with Catalina, said hell with it and reinstalled Mojave. Went in to the App Store, and sure enough, there's all of my purchases.