Currently based on Esri's documentation only Facebook and Twitter support in Hub
Embed video, social media, and iframes—ArcGIS Hub | Documentation
Another untested solution is probably you need to create a simple HTML dan embed an Instagram post then use the HTML that you created to embed in Hub.
Hope, it helps you
Cheers
Obtain Instagram Embed Code:
Hello Esri Community,
I ran into the same issue while working with ArcGIS Hub — Instagram public page links usually aren’t accepted directly because of Hub’s embed security restrictions and Instagram’s iframe limitations. A workaround that helped was using a third-party Instagram widget or embed generator, then placing the generated HTML inside a custom embed card in ArcGIS Hub. It’s not perfect, but it does the job smoothly for public feeds. Also, while searching for simple media tools, I came across Honista which some people use as a free streaming/downloading app companion for Instagram content management.
Thank u!