Displaying a notification to the user with an option to toggle the Show Form option when they open a PDF with fillable forms would drastically improve the UX of this feature. I was previously unaware of Okular's ability to fill in forms until I looked it up on the web and realised that it had this functionality all along. With this very handy feature hidden in the confines of the View menu, it's extremely easily to be entirely oblivious of its presence. Adding a notification could go a long way in addressing this.
Okular has had this as long as I remember. See the attached screenshot. Or am I misunderstanding your wish?
Created attachment 110740 [details] Screenshot with a "fillable forms" info field
Seems to show now. Not sure what happened the other time but I think this can be closed.