ebay is currently rolling out ebay-hosted videos, which (if your video is approved) will show up in the photo gallery section of your listing. This is still being rolled out...not every seller has this yet. Also, the video loading tool is currently only available if you are using the "new" ebay listing tool on a PC (not available for listing on a phone). There are a number of rules that must be followed regarding video size and content.
https://www.ebay.com/help/policies/listing-policies/images-text-policy?id=4240
Do you have this ability? You can check by going to Seller Hub>Listings Tab>Create Listing. Make sure you are using the newest listing form, not the Classic Listing form. After you've filled in the first page with basic title information , click to the next page. Directly under "Complete your listing" you will either see "Photos" or "Photos and Video". If you see the second one, this has rolled out to you, and you can upload your video. Once your video is uploaded, it will say "Under Review" beneath the thumbnail of the video. ebay has stated it can take up to 48 hours to approve a video, and , at peak periods, up to 7 days. Complete the listing form. Upload your listing to ebay. The listing will go live without the video, and once approved, the video will be added to your Gallery (in the second slot).
If this hasn't rolled out to you just yet, you can use the old fashioned way, and put a clickable thumbnail link into the listing's description area. However, I would caution that ebay has not yet stated whether that will continue to be permitted once the new gallery video has been rolled out to everyone...
If you don't have the new gallery video available to you, the way I do it is: shoot your video, upload it to a site such as YouTube, and then create a clickable thumbnail link using this tool at Flippertools:
https://www.flippertools.com/ebayYoutube/embed-youtube-videos-in-ebay-listings.htm
