Save for Web increasing GIF file size (Photoshop 21.0)

I have an mp4 im trying to save as a gif in Photoshop. The original file size is 11.8 MB but when I open it in Save for Web it increases the file size to 140 MB.

Ive adjusted all the settings in the Save for Web menu but nothing really makes a difference other than fewer colors and 0% dither, but its still outrageously high.(dropped it to 64 colors and its at 119 MB)

never had an issue before this last update.

Tried another mp4 file to see if maybe something was just wrong with my file, but i had similar results. went from 568 KB mp4 to a 741 KB GIF.

Installed photoshop 20.0.7 but it does the same thing.

Not sure what else to try.

Am I missing something? 

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