Monitoring Instagram is done by setting up a subscription within the Agility Monitor module. Instructions on Subscriptions are here.
Agility can monitor Instagram posts and reels, as long as the text in the captions or posts on Instagram matches the keywords you have in your Agility subscription search.
For instance, with the below:
The subscription search terms must match the accompanying Instagram caption or text, shown in the red box (not the audio content of the Instagram video, which will not be matched).