You want something similar to “infinite scroll comments”, the difference being more comments triggered by scroll position instead of button click. A search in the repository yields a lot of seemingly false positives, but something in the results might work for you. Or try searching beyond the repository.
In essence, some event triggers an Ajax or API call for another page’s worth of comment data, except the data is inserted into the current page instead of a new page.
Found a plugin called load more anything which has allmost anything i needed.