Are you editing on a desktop or laptop?
When you say click on the video are you clicking on the window or are you actually clicking on the image?
If you click on the image you’ll see a white outline with handles show up around the video. This allows you to manipulate the size and position of the video. On some video cards, the image may degrade as the video card refreshes.
You may also want to check to see what percentage of the picture is filling the window. Right below the image you’ll see a pull-down menu. Much of the time it defaults to “Fit.” Sometimes this can cause issues with your computer’s graphic card. I usually change this setting to 100% to check this out. Usually if the video is at its full size, you shouldn’t see any degradation.
If it’s still fuzzy, I don’t know what to tell you. Render out a small section of video from the timeline to whatever format you want. Shut down Premiere, then play that video with the Quicktime player or whatever video player you like. If it looks fine, I wouldn’t worry too much. If it’s too bad, head on over to the Adobe Forums. Your problem probably isn’t unique.
https://forums.adobe.com/community/premiere/premierepro_current
Hope this helps a little bit.
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“Sometimes Life Needs a Cmd-Z!”