Actually, measured limit of post available to import from Instagram is between 60 and 70.
When I set Import limit to 99 that amount of posts is passed to Joomla (see note at bottom).
I checked plugin code and Instagram API - one important parameter is missed from plugin code - this parameter is called endcursor.
graphql -> hashtag -> edge_hashtag_to_media ->page_info -> end_cursor
This variable contain hashed ID of last imported post.
We can restore import from that point, by passing it to APi query
I tested this feature - it works fine, when I catch endcursor from initial query, I can pass it to next query and get next set of Instagram posts.
All is described in details in this article:
So, there is possibility to import all Instagram posts in loop, by passing each time catched variable form previous response.
Note: As I checked in plugin code, instagram_limit_post variable is probably used only to limit nodes imported to Joomla! at once, not to send this variable to Instagram and limit number of nodes in response.