Shorts videos are regular videos... the only difference between a 'Shorts' video and a VOD (Video on Demand or 'Regular' video) is that they are less than 60 seconds.
That's it.
What happens is that all videos less than 60 seconds get flagged by YouTube as Shorts content. Then YouTube indexes them by performance and includes them on the Shorts shelf. They give preference to videos that feature the #Shorts hashtag, are vertical and have been filmed using the YouTube Shorts Camera.
Your video is a 'Shorts' video. And there is some metric of the Shorts algorithm that takes into consideration past performance when determining the amount of initial impressions a new video will get on the Shelf. But that is about it. The short answer here (no pun intended) is that the video that you referenced here is simply not performing against the videos it is competing against on the Shelf, or YT hasn't indexed it for the shelf yet... something like that. You did nothing wrong, there was no mistake here and the thing that I would advise you focus on for future videos is to keep them around 16 seconds long (that's the average length for the best performing Shorts videos) and aim for a retention in the 300% range. Rewatched content and shares drive success for these videos.