I'd say PDF is all about presentation, while ePub/Mobi is closer to real books that focus on content and legibility.
EPubs are perfect for long-lengthy documents, where you can bookmark position to given line of text (not page, so I'd say it's more precise to get back in which paragraph you've finished reading), everything is searchable/copyable/highlightable, formatted into single-column, usually justified, wrapped using hyphenation, easy to change font size, colors (i.e. day/night mode) and there isn't strict paper (canvas) size. Basically, it increases accessibility and focus.
While the PDF is just like a ZIP (I think those formats share the same popularity), that consist collection of numbered crisp, anti-aliased PNGs and SVGs, sometimes with an attached metadata. I often hear, there isn't any chance to PDF document look different on other device. However, PDF is just a subset of PostScript (hence the name) and has many versions (standardized as a public document, by ISO, by other parties or just paywalled)[1]. Fortunately, quite old PDF1.5 version has majority of features used by typical document creator, also fact that there aren't many competing implementations and they seem to be up-to-date with PDF2.0 convinced users and developers to use it. That's worth noting, PDF supports reflow [0], but it is far from perfect and I guess many bookworms will refrain from using it at all.
Isn't a F11 supported as a shortcut in most of applications to switch to full-screen mode? I remember it was supported over vast majority GUI applications I used, when I was complaining on small screen, but now personally, I don't understand why somebody would need it make windows be maximized-to-workspace as in macOS. There isn't such huge dock, and application menus were redesigned to be in-app-hamburger-menus and finally displays manufactures now provide monitors with higher resolution than few years ago. If you really notice lack of focus / working space, you shouldn't look for typical GNOME/KDE DEs but for a WM (windows managers) like Sway/i3 or AwesomeWM, which helped me to be more productive, when I dab in multiple applications at once.
Could you also explain me if test users generated by dashboard for developers are counted in this 2 billion users claim? I've noticed these accounts aren't in any way logically separated from real accounts. I think there is a lot of apps which uses Facebook services (i.e. OAuth2) which were somehow tested, maybe even by such users.
EPubs are perfect for long-lengthy documents, where you can bookmark position to given line of text (not page, so I'd say it's more precise to get back in which paragraph you've finished reading), everything is searchable/copyable/highlightable, formatted into single-column, usually justified, wrapped using hyphenation, easy to change font size, colors (i.e. day/night mode) and there isn't strict paper (canvas) size. Basically, it increases accessibility and focus.
While the PDF is just like a ZIP (I think those formats share the same popularity), that consist collection of numbered crisp, anti-aliased PNGs and SVGs, sometimes with an attached metadata. I often hear, there isn't any chance to PDF document look different on other device. However, PDF is just a subset of PostScript (hence the name) and has many versions (standardized as a public document, by ISO, by other parties or just paywalled)[1]. Fortunately, quite old PDF1.5 version has majority of features used by typical document creator, also fact that there aren't many competing implementations and they seem to be up-to-date with PDF2.0 convinced users and developers to use it. That's worth noting, PDF supports reflow [0], but it is far from perfect and I guess many bookworms will refrain from using it at all.
[0]: https://en.wikipedia.org/wiki/History_of_the_Portable_Docume...
[1]: https://helpx.adobe.com/acrobat/using/reading-pdfs-reflow-ac...