Is it normal to ask the manager for a proper feedback chat?

Yes. Asking for a short feedback conversation is completely normal, especially if you frame it around improvement rather than selection. Be specific when you ask. Something like, 'Could I grab ten minutes sometime? I'd like to understand what you think I should focus on over the next few weeks' makes the purpose clear. That is very different from cornering the manager after a match and asking why you were not picked. Go in prepared to listen. Ask one or two questions, take the answer away and see whether you can act on it. If you are naturally quiet, this is also a useful step in taking more ownership of your football. Coaches do not always know which players want more detail unless those players tell them. You are not being needy by asking for useful feedback. You are making it easier for the manager to coach you.