Instagram released (at some point this year) an update on their in-app browser (webview) that at least in iOS, breaks most sites.
The attached image is the website opened after clicking the "Learn more" on an Ad, but has the same behavior also on Profile Bio links.
The problem? It seems the top bar is an overlay on the website, making most navigations for mobile (hamburger icon on top left corner) unusable/unclickable and/or hidden.
The innerHeight is the same as screen.height. As answered at How to adjust html/css layout for instagram in-app browser? we can sniff the user agent of the webview.
Unsure if they will fix it at some point, but seems that any padding-top kind of solution would break if they do.