Since you're running PopOS, I believe that's assigned as a "hot corner". I think you can get rid of that somewhere in the settings.

It doesn't appear on mine.

I have a (Firefox) container called Facebook container and it appears for me.

Check if you've any containers that block social media tracking.

@will4623 Can you give us some more info? What do you have running when this appears? What happens when you click on it?

I have facebook container and I run manjaro now. it happens when a page is loading.

There you go. You'll see that little dot whenever Facebook container does its job.

thanks!