By default, the window shows only videos from the last 60 days, so older videos are left out of the initial list. To find them, use the From and To date filters, search by title or ID, or click Load all to fetch the full history (up to about 2 years). Also check the source selected at the top of the window: Instagram lists the profile's videos and Reels, Page lists videos published on the Facebook Page, and Campaigns finds the videos used in ads from the campaigns you select (in that case, choose the campaigns and click Search videos from campaigns). If the video was published on a different profile or Page, change the corresponding account in the section before opening the window.