I have read a lot of treads with the same problem. And I think I have tried to make everything. But Can't still get it to work. I'm new to Blender.
Working in Blender 2.90.1
I have made a character and pressed Ctrl + J. So it's only one mesh. Added the Armature Parented with auto weight so the Armature is pareting the Mesh. And when I go in to Pose-mode and click on a armature och moves it, the mesh don't follow.
What am I doing wrong?