[downeaster59]

I suggest that you look at the Onyx Nova 2, the Onyx Note 2 or the Onyx Max. The Max is the largest and most expensive. You may find a 13 inch display a bit too cumbersome. The Note has a 10.3 inch display which is ideal for pdfs.

I have the Nova 2. It has a 7.8 inch display. That is a good compromise for me. It's large enough for the pdfs I read - especially when I use the crop function to reduce margins and make the text as large as possible. The Nova 2 is also a comfortable size for reading eBooks. I found the Note a bit too big for extended reading, though it is not at all heavy for its size.

These Onyx devices all run Android 9.0. You can install Libby on any of them. All use the stock Onyx browser, which is fine for me, but you can install other browsers if you like. You can install Pocket or Instapaper or the NYT app. All work well.

I can't tell you how any of these devices accommodate people with vision impairments, as I'm not sure what accommodations you would need. You can adjust the system font size, for one, by making it larger. Hopefully, others with experience can help you with this question!

Kobo devices have a browser and Pocket. I don't know about Libby, though.

Likebook offers a line of readers similar to Onyx. Likebook devices are good, but I'd rate Onyx a bit better across the board.

Edit: I was just playing around with the pdf settings on the Onyx native reader. There are a number of ways you can make the text larger. It has reflow mode, which works well enough but could use a little more refinement!