Sorry, I was wrong with my previous post as I learned later in a different thread. I can confirm that the built-in display DOES work without a firmware blob. It only seems to be needed to get the external display working. See also this thread:
https://forum.pine64.org/showthread.php?tid=12534
I am pretty sure external display would work with a usb adapter as well if you find one that works without blobs. However, I am not familiar in this "market". Do you have a particular model in mind?
Edit: Regarding other blobs - I am not sure whether u-boot ships a blob for training the DDR4 RAM and there is also something for using DRM in the trusted firmware repo. I've heard about some script to clean this repo (comparable to linux-libre) but I did not test this myself.
https://forum.pine64.org/showthread.php?tid=12534
I am pretty sure external display would work with a usb adapter as well if you find one that works without blobs. However, I am not familiar in this "market". Do you have a particular model in mind?
Edit: Regarding other blobs - I am not sure whether u-boot ships a blob for training the DDR4 RAM and there is also something for using DRM in the trusted firmware repo. I've heard about some script to clean this repo (comparable to linux-libre) but I did not test this myself.