Thanks for uploading the sprite sheets!
To answer your question, Unity doesn’t limit us to JPG. We can use various formats like PNG, JPG, and others.
Also, in most cases, Unity developers prefer sprite sheets over GIFs. GIFs are not commonly used directly in Unity because they don’t integrate well with the animation system. Sprite sheets are much more efficient and give us better control over animations inside Unity.
So your sprite sheet approach works perfectly