Hello Skoonydude,
Since you are seeing them in iCloud, this would indicate that you are using iCloud Photos.
This information from Share photos and videos and keep them up to date with iCloud - Apple Support explains how iCloud Photos works:
iCloud Photos
When you set up iCloud Photos, the photos and videos on your device are uploaded to iCloud. You can still see them in the Photos app on your device, and any photos and videos already stored in iCloud—for example, from another device with iCloud Photos turned on—are added to Photos.
You can see your photos and videos on any device that has iCloud Photos turned on, including your iPhone, iPad, iPod touch, Mac, Apple TV, or Windows computer. You can also access your iCloud photos and videos in a web browser.
Because your photos and videos are in the cloud, changes you make on one device—like taking a new photo, cropping a video, or deleting a photo—automatically appear on all your devices. You see the most up-to-date versions of your photos and videos, no matter where you access them.
If you delete a photo or video stored in iCloud Photos, it’s deleted from all your devices. Photos and videos you delete are moved to a Recently Deleted folder in Photos on your iPhone, iPad, iPod touch, and Mac, and on iCloud.com. Recently deleted photos and videos can be recovered for 30 days. If you permanently delete a file from the Recently Deleted folder, you can’t recover those photos or videos.
There are some iCloud settings that can affect playback.
Tap on Settings > [your name] > iCloud > Photos.
Optimize iPhone Storage is most likely selected. If you change it to Download and Keep Originals, the videos and photos will be stored locally, on the iPhone. Of course, this could use a large amount of the storage available on the device.
With Optimized iPhone Storage selected, you should be able to tap on a video, and it should download the original version. You should then be able to play. The better the network connection, the faster the download.
Last thing we would like to emphasize is that iCloud Photos is a great syncing service that allows you to share your photos and videos amount devices. With that in mind, it is recommended that you back up all those memories somewhere else, as a precaution. Here is information on how to do that: Transfer photos and videos from your iPhone or iPad to your Mac or PC - Apple Support
Have a good day.