It looks like some of the vertices of the biceps are influenced by several bones, if you select one vertex of this zone and open the N panel (on the right of your 3D View) > Item tab > Vertex Weights, you'll see a series of vertex groups that the vertex should not be part of.
Also, if you select your armature and go in the Properties panel > Object ...
That looks like your issue. I googled "copy weight paint blender" .
Go to 'Weights'>'Transfer Weights' from the menu to the left of [Weight Paint]