I don't think that's possible. But if you annotate outside of Evernote anyway, you could use one of several options (at least on Mac and iOS) that are more powerful, like Highlights, LiquidText, or Marginnote.
Hopefully someone has a better answer but I don't know of anything in landscape to view side by side.
You could open 2 windows of GoodNotes and then run the two windows side by side. Kind of a pain as you'd have to scroll both windows.
Check out this GoodNotes support article on multiple windows on iPad.
Have the same document open. The windows scroll independently which is a pain if you are just reading through a PDF.
You could also switch to Vertical scroll which would allow you to zoom out and see multiple pages.
Contact GoodNotes - they do keep track of frequently requested features.
I've found GoodNotes to be an excellent notebook replacement. For use cases like studying from PDF - I like to use MarginNote. LiquidText is another similar app but I find myself using MarginNote as I like the way it generates mind maps.
I have diagnosed ADD, and would be happy to discuss citation/note-taking strategies with you over PM and/or continuing this thread, if you'd like! Zotero pairs well with Zettlr, so adding Zotero onto your current workflow shouldn't be too much of a hassle!
I use an older iPad Air along with the original Apple Pencil, and haven't encountered major issues. So, if you're open to buying outdated/refurb devices, looking at older iPad Air/Pro models might be something to look into.
Re: apps: I've been trying out LiquidText and MarginNote, since I like having my notes and the original text side-by-side. Unfortunately, I'm not particularly excited by either of them, yet. Can't quite explain why aside from that their marginal value added < the cost of further complicating my workflow.
I made the switch to an iPad Pro last fall. To get around the USB problem I used a combination of AirDrop (if I was working with people using Macs) and Dropbox. Other clouded services like Google docs and Microsoft 365 (which I do not use, but are options) are a big help.
If you plan on using an iPad Pro for notes I cannot recommend Liquid Text (https://www.liquidtext.net/) & Margin Note 3 (https://www.marginnote.com/) enough for organizing research as well as annotating PDFs and ePubs.