In short, use the following command to do the conversion:
ffmpeg -i source_file.m4v -filter_complex "[0:v] split [a][b];[a] palettegen [p];[b][p] paletteuse" output_trimmed_enhanced.gif
Reference: https://www.bannerbear.com/blog/how-to-make-a-gif-from-a-video-using-ffmpeg/