On most phones, for example, the whatsapp or Instagram messages are displayed directly on the lock screen, I've now added a Huawei mate 20 lite & this only shows me that I have a message in the app. Can I change that somehow?
Yes on my Samsung this is: settings, notifications (you can set which apps you want to see), advanced notifications (which will be displayed, hidden or blocked)
Do you have to see if it is the same with you?