same here, I can't reverse the update
what I did
1. to play videos on Gallery → I tap the below centre thumbnail (of video) to expand → then I can now slide the video forward or backward
2. or tap 3 dots → open in Video Player
3. or download Samsung Video Library app from Play Store → there I can manage videos, it's a very small app, only 5MB. It plays instantly too
@DannyP: You can also access an archive of your videos by opening the Gallery app > Tap the 3 lines in the bottom right > Videos. Tap on a video thumbnail, then select 'Play Video' at the bottom of the screen, using the forward and backward arrows to cycle through. Alternatively, tap the Mute button in the bottom right of the screen to enable audio, and swipe to cycle.