If anyone else went searching for this:

https://imgur.com/RVVnTNR

Wow, that is surreal!! Do you know what algorithm is being used?

I don't know. I've found a few discussions on Reddit and elsewhere, but everyone seems to credit this particular Imgur post with no context as the source:

https://www.reddit.com/r/oddlysatisfying/comments/bikp2u/tom...

https://www.reddit.com/r/interestingasfuck/comments/biixsf/t...

https://www.youtube.com/watch?v=labEXi5nOso

That looks awful, tbh. Sure, the smoothness is there, but it's also full of distracting artifacts.

They're decent in terms of image quality, terrible in terms of animation.

Aside from the obvious problem of motion interpolation having problems with acceleration/deceleration, there's a lot of nuance in the original animation that gets lost when you try to interpolate from one sprite to the next.

Even if you can avoid obvious artifacts, no interpolation algorithm can create new information, it can only derive from what's already there and guess at what's missing.

EDIT: If you dig through twitter you'll find some tweets from animators explaining why the results are bad. As mere consumers we might be tempted to dismiss that criticism as snobbery but animating is a craft and the interpolated results are objectively worse than the original.

When I read your comment, I asked myself if vector conversion could be a solution.

Old cartoons lend themselves to be converted to vector images and these are better to animate automatically.