I think most GIF optimizers would do it, although I haven't tried any. E.g. https://ezgif.com/optimize https://ezgif.com/optimize says they do it ("makes unchan

I think most GIF optimizers would do it, although I haven't tried any. E.g. https://ezgif.com/optimize https://ezgif.com/optimize says they do it ("makes unchanged parts of the following frames transparent").