This seems to be changing. I have an older Paperwhite; my GF has a newer one. I uploaded MOBIs to both last night (via USB) - it worked on hers, and they didn’

This seems to be changing. I have an older Paperwhite; my GF has a newer one. I uploaded MOBIs to both last night (via USB) - it worked on hers, and they didn’t show on mine. I had to convert them to AZW3 and reupload for them to show in the listing. (I’ve not checked, but it’s plausible my older model has more up-to-date firmware.)