I was able to add an App Store Connect API key on the Integrations tab on the Users and Access page in App Store Connect. I was following the instructions at https://zcusa.951200.xyz/en-us/dotnet/maui/ios/apple-account-management?view=net-maui-8.0 which apparently is already out of date. It doesn't mention or show in the images that there are now separate sub-tabs for Team Keys and Individual Keys. I took a guess and generated a team key.
When I tried to add an Enterprise Account in Visual studio, I got the error reported in this thread. Oddly, Visual Studio will let me create an individual account using the Team Key I generated, but of course, I don't see my enterprise group.