Maybe your previous purchases have been hidden?
The App Store application is the starting point for reinstalling your apps. Launch the App Store app then click the Store menu > View My Account you will be presented with the Account window showing "Purchased". There are two options at the top right of that window; View Information and Redeem Gift Card.
If you click View Information you will be prompted to enter your Apple ID and password. The Account Information window will now appear and you will see a section called Hidden Items. You'll see Manage Devices and Hidden Purchases. Click Manage next to that and see if your previous purchases are hidden. If so, simply click Unhide and then click Done.
And btw, the iTunes app is no longer. I believe is became simply the Music app in Catalina. Just sayin'. If your app is still named iTunes, then there's something bigger going on.