Thanks mdp.
In the mean time Onyx confirmed what I though: that my M92 will not perform well with an external keyboard.
I still think the Boox Laptop was a good idea. But I very much like the looks of the "Onyx BOOX Canvas":
https://www.youtube.com/watch?v=u2eKxeR2uHE
I guess I'm used to my white M92. But the Canvas screen is a bit lager, and would be perfect for writing with an external keyboard. For typing texts in documents so far I use the free version Jarte on my laptop. Jarte is like WordPad but has extra features like spell checking, word count etc., and the Jarte documents can easily be converted to PDF with a click (tap) or two. The width of the Jarte page I write on would nicely fit within the frame of the Carta. So I'm already used to that width for writing, although I can zoom it wider using 2 fingers on my touchpad, but never do. (The max length of sentences in Jarte is 16 cm or 6.5 inches on my laptop 15.6" screen when not zoomed wider.)
So now I wonder whether the Carta can also be used with an external keyboard. I suppose it can.