AppStore logged in but repeatedly asks for iTunes login without fields for username or password

iMac, OS 14.4.1

Need to update Logic Pro. I click the update button in AppStore. It asks for my login. I enter username and password. Then another pop-up appears saying I need to log in to iTunes. But it doesn't have login fields. And I'm already logged in! It has a download button in the popup so I click that. But the same popup appears again. And the same happens repeatedly with no way past this point. I've seen similar problems going back to 2022. Why is this still a problem?

Fix it or give me a workaround please.