Books won't split screen on Mac

I have a MacBook Pro and always watch a show while reading a book. I went to split screen my book with chrome (which i never have a problem with, unless chrome needs an update) and it wouldn't work. I did mess around with my settings because i have just set up a monitor and i'm worried it might be that.

I checked the mission control > allow spaces thing, which is on.

I can split screens for everything else, just not books, so I think it may be the application itself.

Please let me know if there are any other troubleshooting methods I can use.