I do know there's an option to make okular ask backend whenver open a document and this is not convenient because it asks WHENEVER open a document even though I only want a specific backend. An option to set backend to open a document would be helpful. Reproducible: Always
Make sense, should not be that hard to code. if you have some coding experience, maybe you want to try it?
I've never worked with KDE source code. Anyway, I've looked into source code of Okular and I noticed that it's not easy to implement this feature because a backend for a document is 'queried' by document type. I think a checkbox list for backends to enable/disable a specific backend would be more easy to implement and also it will not cause conflicition with ChooseEngineDialog-related code by eliminating disabled backends from offer list.
Well, why not a list of all the mime types okular can open with more than one backend and letting for each of them sort the possible backends?