A product video that uploads fine but never appears on the storefront usually comes down to one of
Most missing videos are still processing, sit in Files instead of on the product, or are below the fold in the gallery.
Product cards on collection pages show a still frame for video media in Dawn and Horizon, which is expected behaviour, not a bug.
Buy Button embeds render images only, so a video on the product will not appear in an embed on an external site.
Older themes that loop over product.images instead of product.media skip videos entirely and need a small Liquid change.
The most common reasons are that Shopify is still processing the file, the video sits in Files rather than on the product's media list, or the theme renders product.
The full guide has the formats, the deadlines and the worked examples.