If a person wants to discard old quran or a surah of quran, can he do so my using whiter or black out or scratch out the verses so it’s no longer "visible" and then discard it like regular paper?

I know about the method of throwing Qur’an into clean river but is the quran still a quran if you cross out all the verses? Or is it haram to use white out on the quran to erase the verses?

Yes you can scratch it out or put whiteout. However even after doing so, one should not throw it in the trash and discard it in a way which would not seem to be showing disrespect to the Quran.