Is it possible for you to share a copy of the notebook you have in the screenshot with a page for every monster for download? I own the books legit but I've been putting off making my own notebook like that because it's a lot of work

Unfortunately, i dont really share out my personal notebook due to piracy concerns, coupled with the fact that oneNote pretty liberally plasters in your personal information. That said, there is an SRD oneNote notebook that exists as a good starting point here (its what i started with years ago): http://www.cryrid.com/digitaldnd/

Also, if you have PDFs of the supplements you want to add, you can very easily insert them in to oneNote as a printout (just make sure to turn on the option to make each page of the PDF its own oneNote page), and then you just have to manually rename pages. The inserted PDF pages are printouts (basically images) of the PDF pages, but they're still text searchable.

Additionally, i've been considering coding this extension to allow for the import of lion's den 5th edition apps because i know a lot of poeple use that as a backup format for D&D related stuff (and i believe there are potentially less than legal-ish copies of official stuff shared online) and coding it to insert oneNote pages into your notebook. That's actually on my to-do list right now, because i've started updating some more functionality on this plugin recently, as i've had a chance to return to it some.