I am using the trial version of Adobe Captivate 2019.
I am unable to trim / split a video inserted in one of the slides.
Does Captivate disable Trim/Split video feature in its trial version, or I am missing out something.
Nothing is disabled in the trial version. But you seem to think that Captivate is a video editor instead of an eLearning authoring tool? It has never been meant to edit video. You have a trim and split feature for Full Motion Recording slides in software simulations. You get a more complete video editor after having used the Video Demo to capture a screen recording. But from your question it looks like you want to edit imported video?
Video can be imported as event video and as slide video. The first type has no editing possibilities since it is just playing independently of Captivate's timeline. Slide video is synchronized with Captivate's timeline. You can distribute the video over multiple slides. By decreasing the duration of a slide you can cut the end of a video. But if you need real video editing functionality you need an application like Premiere Pro, not Captivate.