GoodNotes: Six ways to open multiple instances in iPadOS

1. Pick an open tab and drag it to the where you want your second instance. 
2. Use the split view icon on the right corner of an open tab. 
3. Open a new document (on the homepage) into a new instance. Tap downfacing arrow on notebook > open it in a new window. 
4. Pick up a document and drag it to the side. 
5. Select a specific page to open from the document’s overview. In this window, pick and drag the page you want in a new instance. 
6. My least favourite option: drag the app from your dock.