Pin Link To Taskbar [exclusive] -

This package contains a manifest.json and the site’s service worker. The taskbar icon becomes a full PWA, capable of offline operation, badges, and notifications.

%AppData%\Microsoft\Internet Explorer\Quick Launch\User Pinned\TaskBar\ pin link to taskbar

You can force any URL or even a document to be pinnable by creating a custom .lnk file with the right properties using PowerShell: This package contains a manifest

Are you trying to pin a (like Gmail or Slack) that might have a dedicated app? capable of offline operation