Selecting the Project Track to Insert Frames in the Project will insert frames, but only one Track (not sure related to which logic) is shifted after the cursor position. All other tracks are not moved, which makes the feature unusable. The exact same operation works as expected in IClone 7, doing the same there results in all tracks being shifted, as expected when "Insert Frame" is selected from the Project track.

So yea, this is irritating.  I see it has been added to the feedback tracker where RL says its not a bug:

"This is our current specification that clips will be not inserted. The behavior of other 3D tools is also the same. If the specification is modified, it may lead to unexpected errors, so we decide to maintain the current specifications."

This feature doesn't seem to work at all.  You have to select the item in the timeline to add the frames to but the frames seem to be added to the project level of the timeline even when its x'ed out/deselected.  Therefore if you try to add frames to individual items the project gets added frames every time.  This seems like it was functional and useful in Ic7 but now not so much.

It actually works fine for me in IC8, the same way it used to works in the last IC 7.93.
Yes, continues clips are not getting stretched and I could understand given complexity behind internal key maintenance specially in the latest iClone.
But all other keys like Transform, Materials, Reach, Constraint, Visibility.. etc are shifting while frames are added.

And if clips must be split/shifted, I'd recommend using a Break at the frame where frames are added (before adding them).
At this point the right portion of the "broken" clip would be shifted further to the right.

Thanks for the reply.
So it’s adding clips frames for every item in the scene? Also if you can please verify that it works for constraints and expressions (edit- I see you mentioned constraints in your post). as it doesn’t do so on mine with selected items.

Yes all was working in my tests except solid clips such as motion, animation, expression. Those need a Break at the frame insert point.
Here is a quick rundown.