I find it difficult to do = I have experience doing the action, and I think it is difficult based on my experience so far. It is difficult to do = This sentence has no extra nuance. It is an impersonal statement (statement without a subject) that the action is difficult.

For me there might be a very slight difference. "It is difficult for me to do" says I have trouble commencing this particular exercise, maybe because of some other clashing commitment, for example. "I find it difficult to do" describes a more general, continuing situation, whereby every time I engage in this activity I find it difficult. The difference is really very subtle, though, and you could almost use these two interchangeably.

Hi there, Yuta. they are basically the same thing, one's just more of a "proper" and older way of saying it, you're probably more likely to hear "I find it difficult to do", but they have the same core meaning and are different structures of the same sentence/idea