So I remember someone posted something similar a while ago and I also remember that Mike said to post about problems if they also have a problem with animation (could be remembering wrongly also because my brain is dead recently) this is the problem thanks 1740D - Knowledge Cards
https://codeforces.me/problemset/problem/2002/C
Same with this Ig
Trying to open the Testcase explanation image in a new tab gives this PNG: https://espresso.codeforces.com/762b4fec0fd1a6b4150f305d2407db01f71c3306.png
As PNG cannot show multiple frames like a GIF, it should be expected as a still image. In case a PNG preview has been generated out of an uploaded GIF, the problem setter may provide the multiple shots separately or somehow share the GIF instead.
It may be an APNG:https://codeforces.me/blog/entry/124035
That's a good reference. Thank you for sharing it.