Please I will be happy if you can help me, this is my first time trying animation and this is the third day I have been clicking bake and surfing online for solutions

youtube.com/watch

this answere is maybe like your question ;)

think you should consern the name conventions, this might be the problem.

if you don`t get it working ask the mixamo addon developer.

or maybe a workaround is to save the file... disable the mixamo and bake it like it should be done in blender for armatures...

with the rig selected go to pose mode>pose>aniamtion>bake action