How can I backup more apps in Icloud?

You mean backup more app data (not apps), right? This is what iCloud backs up -- What does iCloud back up? - Apple Support. Do you have enough iCloud storage to create these back ups?

Apps themselves do not live in anyone’s personal iCloud storage quota. They live in Apples App Store which is itself a virtual store in the cloud (but not iCloud). Only your app’s data is stored in your iCloud space.