When someone apologizes for talking too much, they usually weren’t. Tell them you liked hearing it.

Somebody who apologizes for taking up space has been told at some point that they do. They are checking whether you were being polite or were actually interested, and a vague reassurance leaves the question open, so next time they stop earlier. One clear sentence answers it.

Tell them plainly that you were enjoying it, then ask the next question. Naming the specific part you liked makes it impossible to read as manners. People who were taught to apologize for talking tend to remember whoever told them not to.