Here is some information
Standard YouTube channels
Videos uploaded after October 15, 2024: Any videos uploaded on or after this date with a square or vertical aspect ratio up to three minutes in length will be categorized as Shorts on YouTube.
Videos uploaded before October 15, 2024: Any videos uploaded before this date will remain the same, as a long-form video on YouTube.
Official Artist Channels
Videos uploaded after December 8, 2025: Any videos uploaded on or after this date with a square or vertical aspect ratio up to three minutes in length will be categorized as Shorts on YouTube.
Videos uploaded before December 8, 2025: Any videos uploaded before this date will remain the same, as a long-form video on YouTube.