Hello ProPauli,
Welcome to Apple Support Communities. We understand that your videos are not playing in full resolution and show unsupported file error. We’re happy to help.
Have you optimized your photos and videos to save storage? Here’s more on managing photo and video storage: Manage your photo and video storage - Apple Support If so, when you download the video, are you able to view it in full resolution? here’s how to download the videos: Download iCloud photos and videos - Apple Support Were these videos recorded with your iPhone? If not, what device did you use to record the videos?
These answers will assist us in isolating the cause to get on a path to a resolution.
Let us know the results.
Take care.