This is a 5000km circle centered around Paris.
Found here: https://m.facebook.com/photo.php?fbid=924622615693114&id=100044361527327&set=a.610868297068549
We have Tissot’s indicatrix to display this kind of distortion, much more universally usable than this random circle. Check wikipedia for examples, scroll down: https://en.wikipedia.org/wiki/Tissot’s_indicatrix
If you want to play with it yourself and compare countries.
There are a few interactive maps you can play round with online. Search for “mercator distortion play” to find one that clicks best with you.
But even then it looks like Greenland is still larger than Australia. Is that true?
No
The map is just the mercator projection, but it’s showing a circle to show how distorted it is. If this was shown on a globe. The circle would look like a circle and greenland would look much smaller