Shorts grow a channel when the next click exists
A Short can be watched by people who have never seen the channel. That only becomes growth if the viewer can tell what the channel is and what to watch next. The related video, the playlist, and the channel trailer do that job. A subscribe animation at the end does not, because the viewer still does not know what the next upload will be.
Treat each Short as one claim from a longer video, or as a standalone answer that names the series it belongs to. "Part 2 is on the channel" is a reason to look. "Link in bio" on YouTube is a habit imported from the wrong app.
The first second and the loop
Start on the result or the problem. A logo, a "what's up", or a zoom into your face with no words is a swipe. Put the topic in the first words on screen and in the title. Shorts search still reads the title. A title that only says "wait for it" throws away the people who typed a question.
If the Short loops, the last frame should match the first so the replay feels like one thought and not a jump cut. Loops help when the idea is a single visual change. They do not rescue a Short that never said what it was about.
Pick a slot, then believe your own analytics
Publish when your viewers are opening YouTube, which you can see in YouTube Studio under Audience. If the channel is new and that chart is empty, use the free Shorts posting grid as a test: one lunchtime Short and one early-evening Short, same kind of idea, and compare average view duration rather than the view count alone. A higher view count with a worse percentage watched is the weaker video.
Public tools cannot see that chart. Creator Climb does not invent it. On the Unlimited plan a connected channel can add read-only YouTube Analytics for watch time and net subscribers. Click-through rate is still not in that feed, and we do not show a number we cannot read.
What to do with the long videos
When a Short works, the long video on the same topic should already exist or be the next thing you film. The title of that long video has to make the same promise in words a stranger understands. Run it through the title generator if you are stuck, then the channel audit if you want the pass done against the uploads that are already public.