How to say "自身的兴趣“ in English
Not knowing the context, I would guess that ‘personal interest’ is the best way to express this.  People have professional or academic interests that are connected with work or studies.  In contrast to those, they have hobbies, and these are their personal interests.

‘Inherent interest’ is different – a student could say ‘I’m learning about plant genetics at the moment, but the topic has no inherent interest for me.’  He or she isn’t interested in plant genetics for its own sake, but just to get a good grade on the exam.  I’m not sure how to get this nuance in Chinese though.