All depends on the animation. You will have to convert the gif from Indexed to RGB for the attached script c2a-all-layers then re-export as a gif.
...but that can introduce semi-transparency in some remaining colours.
...or non-Gimp using ImageMagick try (change -fuzz percentage as required, not even sure it is required for a gif
)
...but that can introduce semi-transparency in some remaining colours.
...or non-Gimp using ImageMagick try (change -fuzz percentage as required, not even sure it is required for a gif

Code:
magick infile.gif -fuzz 10% -transparent white new.gif