We already added tracking to some mobile apps with the old 4.x Adobe SDKs, but newer apps from newer development platforms (e.g. Flutter) cannot use the old mobile SDKs. We would want to switch to the new mobile libraries from Adobe Launch, but not sure if this is possible. We use Adobe Launch, but not AEP yet.
I don't think you need an additional license.. but you may need a new Mobile App tracking server to be configured for your mobile app.
This would be a good conversation with your CSM... they will know what your contract includes and be able to advise you on how to start transitioning... but, since you already have a mobile app, and you are using SDK 4.x, my feeling is you already have what you need.
We are using SDK 5.x, but we are not yet using the Edge server.. we are using the Analytics extension.. but then again, when we built our apps, that was the only option..