How to highlight object in render?

How to highlight object for render? I need to do video about technical piece, and when narrator mentions some detail, it should be highlighted.
Maybe there’s some kind of overlay like lines around object? (I heard about freestyle, but didn’t understand how to set it up properly) or maybe set material on top of other materials and animate it’s transparency?

I have no idea if this works, but I would consider trying highlighting it as a glow. Same camera angle, render out in isolation; first with emission only based glare post process, then with a holdout you subtract from the glare, which is then added to the actual render. You might get away with rendering out just the holdout and doing everything in post based on that mask.

Freestyle to me is just too time consuming, it can take hours for complex scenes. I’m not happy at all with it’s sorting speed on what to consider and what to just drop.

Freestyle would be the easiest solution, just create a new collection and set freestyle to “Select by collection” and put the object to highlight in that collection.

The other solution i can think is render the object to highlight alone with alpha background and mix it in the compositor with an complete scene colored gray for example.

Many video-editing systems already have this capability built-in, since it is so commonly used. (Of course, with footage that isn’t CG-generated.) I don’t know if Blender’s video-editor has it, but there are plenty of good open-source as well as commercial possibilities which should have it.

What you wind up doing is basically to hand-draw a mask. This mask is then blurred and superimposed on the image, as a strictly two-dimensional effect. I think that this approach would work just fine for your project: there should be no need to do this “in the render.”