after importing a video it glitches (like the one on televisions)

Let's eliminate some things:

• In Composition > Composition Settings, what's the backgroud colour?
• If you play a video outside of AE, does it play correctly?
• What happens if you try to convert a video by adding to to Adobe Media Encoder and exporting it from there?
• Have you set the project to Mercury software only? (under File... Project Settings)
• When you say it happens on all the files, have you tried just downloading an image from the internet or are all these files coming from a particular source.  The second screenshot looks a little like it might have come from TikTok and I'm just trying to make sure this is occuring to all files.
• What happens if you make a new comp and use a shape layer?  Does that render out and does that import?
• Have you tried uninstalling After Effects and reinstalling it?

At the end of all that, my gut feeling is it's a corrupt install of AE or possibly just your media cache.