That NXTPAPER 14 looks interesting. It seems the matte anti-reflective treatment is well done and looks like it doesn't mute colors or introduce much graininess.
Is there a pen available for it?
The best implemented matte treatment I've come across so far (without seeing the device in person) is the Huawei MatePad Pro :
https://youtu.be/cIkrjAfBUCk?si=J56lObsYaFgpLdj_