Depends on the person who you are talking to. In a research group which is not exceedingly interdisciplinary, it might deviate from what your professor is looking for and thus it might be a downside for the person who is evaluating the applications. If the group is searching for variety, it might be beneficial to state the different fields in which you are interested.

In a more practical way, look to the research group itself: if it is way too large, it might not be a disadvantage but take a good look into their research fields! If they are concentrated in a single topic, it might be good to introduce the difference in scope after you are used to how does that particular research group work.

Depends on the person who you are talking to. In a research group which is not exceedingly interdisciplinary/varied, it might deviate from what your professor is looking for and thus it might be a downside for the person who is evaluating the applications. If the group is searching for variety, it might be beneficial to state the different fields in which you are interested.

In a more practical way, look to the research group itself (and, as @aparente001 just mentioned, their publications): if it is way too large and its publications are wide-ranged in topic, it might not be a disadvantage and it can definitely turn the balance in your favor. Nevertheless take a good look into their research fields! If they are concentrated in a single topic, it might be good to introduce the difference in scope after you are used to how does that particular research group work.

Anyhow, never be too specific: the field you are speaking of has a lot of interesting research opportunities and you can end up researching a field you had no idea you were interested in.