20.04.2. I just uninstalled my windows 10 and I'm feeling much better already. I would like to have thumbnail preview icons for all types of picture formats and video formats. I would also like to see a briev folder icon preview of whats in that folder. Currently .jpg and some other formats have a picture preview icon but not .webp formats, and I'll probably find other formats also not having a preview icon.
First try installing restricted codecs for your operating system. Simply search online for directions for your OS. This way the OS can read the files on its own. Then update in app store. Reboot. Test by copying, pasting a video file to desktop. If you see video thumbnail it worked. You just need to refresh thumbnail cache at that point.
I reset thumbnail cache by going to ~/.cache/thumbnails and deleting the images in the folders forcing system to refresh them.
I did this in PopOS and it worked, which is Ubuntu based so should work on Ubuntu also.