I think in the last few months / years data privacy (especially for Facebook) has become a big issue leading to much more limited API calls to social media profiles. The days you could simply call for any insta post comment or tweet are over
You should read Instagram's API page to see what you can get these days or not:
Probably that R package stems from days the restrictions were not in place. From what I can read now, you can only get media and comment data with explicit permission of a user, otherwise only basic profile info is available.
The only way you could get comments now would be through actual webpage scraping on profiles that are public or you have access to, but you'll have to write custom scripts to extract that data and I don't know how difficult that would be.
Hope this helps,