Today I had to print a document in a network that had more than 4 printers. Okular seemed to find all of them successfully, but only display 4 (seemingly in an alphabetical order) with no way to choose the one I needed.
Created attachment 109169 [details] I have added 8 dummy printers (https://superuser.com/questions/304670/how-to-add-a-fake-dummy-null-printer-in-cups) and okular print dialog detected only 5 initially Okular print dialog detected only 5 printers initially but after i opened the print dialog again after running lpstat, it detected all 8 printers. I tried this with 13 dummy printers also and it detected only 10 initially but after some time it detected all 13 printers.
Okular doesn't have anything to do with the printing dialog, that is provided by upstream Qt, so i'm going to close this bug. I guess you can reproduce this problem with other Qt apps like assistant for example, you should open a bug in qt bug tracker at https://bugreports.qt.io/ but take into account that at the moment there's not really a maintainer for the printing dialog. FWIW I tried it adding 13 fake printers like you mentioned and i got them all, but on the other hand i have no network printers, so i guess the problem may lie in the networking side of it.