YouTube: custom thumbnails for Shorts

Since July 2026, YouTube lets Partner Program channels set custom thumbnails on Shorts. Today Zernio skips the thumbnail on Shorts ("Custom thumbnails work on videos only, not Shorts"), so we have to set every Short's cover by hand in YouTube Studio after it publishes.

Request: when a Short has a thumbnail on its video media item, set it once the Short finishes processing (for example with thumbnails.set). If YouTube rejects it, skip it as you already do for regular videos on unverified channels, and publish the Short anyway.

Use case: a newsroom publishing several Shorts a day from a planning tool. The cover is part of the brand design and is prepared before the Short is scheduled.