[ManlyBread]

>a lot of times i feel my mind blank like i have nothing to say (in serious and non-serious conversations)

I know this feeling. I manage to overcome it by practicing small talk and being less afraid of voicing my real thoughts. For small talk any topic is fine, no matter how short and mundane. If you get into a habit of practicing small talk at every occasion it should help you talk about the things you actually care about. For expressing my real thoughts I've stopped giving "calculated" replies (like changing the wording in order to not upset / offend anyone) and started caring less about what other people think of me.

>having difficulty forming opinions besides on basic black and white topics

Go to any discussion board, pick any topic and play devil's advocate. It will help you interact with opinions that you disagree with and make you evaluate takes you wouldn't evaluate otherwise. This is especially effective if you pick a stance you personally disagree with.