I’ve been getting extremely evil thoughts for years now and I want them to never come back please give me practical help to eradicate this from me. I’m also curious to know if these thoughts are from shaytan or from my nafs.

Try to always do thikr using the beautiful names of God.
They could be from Satan or nafs. Recite this frequently:

يا الله يا رحمان يا رحيم، يا مقلب القلوب ثبت قلبي على دينك