Shorts & Vertical Video
Cannibalisation
Also called: do Shorts hurt long-form
The fear started from something true. When Shorts launched, a viewer who watched a long run of them could find long-form vanishing from the main app entirely, so YouTube separated short-form and long-form watch history into different signals.
What is left is a packaging and expectation problem. Somebody who subscribed off a 30-second video has told you almost nothing about whether they want your 20-minute one, and a channel page dominated by Shorts can bury the long videos those Shorts were meant to feed. Judge each format on its own reports over a few months before deciding either one is costing you the other.