Shorts are a format, not a separate video store
A YouTube Short is an ordinary upload that meets two conditions: vertical or square aspect ratio and a duration under three minutes. It gets its own player surface and its own /shorts/ URL, but the file behind it lives in exactly the same system as a regular video.
That has a practical consequence: a /shorts/ link and a /watch?v= link with the same ID point at the same media. If one fails to paste cleanly, the other form usually works.