I haven’t tested it in UE but i believe the scale is set in the animation keyframes. I’m unfamiliar with how UE’s animation systems work but if you open the .BLEND file and find the animation keyframes you should be able to delete the scale keyframes and re-export the file. This may also be possible within the UE editor but i am not certain. (you can do that kind of stuff in godot or unity)
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I looked at the .BLEND file and it does not seem that scale is baked into the animations. This may be an issue related to import settings with UE5 or perhaps a bug within the UE sequencer. Scaling the character with animation seems to work in other programs.