Select a poster frame for video thumbnails in Photos app?

Is there a way to select a Poster Frame to use as the thumbnail of a video in your Camera Roll?

For example, many of my videos fade up from black. Because of this, the thumbnails are black and it's difficult to distinguish between videos. It also looks bad if a business is presenting videos to potential clients on an iPad.

Can video poster frame thumbnails be added on iOS(preferably) or Mac?

You can set Poster Frames via Photos.app on macOS.

Setting via the Mac does sync the custom poster frame to your iOS devices via iCloud Photos.

1. Play a video in Photos for Mac
2. Pause the video at the intended frame
3. Press the gear icon and select Set Poster Frame

In macOS Big Sur, the gear icon has been removed and this feature has moved:

1. Press the Edit button.
2. Scrub to the intended video frame.
3. Select Make Poster Frame from the pop-up.