Assalamu alaykum wa rahmatullahi wa barakatuh Ustadh Ahsan Allahu ilayk I am worried because I have heard that disliking Polygyny is kufr and I'm scared that I do dislike it because I often get negative feelings when I hear about that. I'm scared I have become a Kafir.

Ustadh AbdulAziz al-Haqqan

This is jealousy not hatred towards the legislation of Allah. I also advise you to reconsider your position as the wellbeing of society is in what Allah has legislated