You must have parented with the With Automatic Weights mode, therefore some vertices of the body will be assigned to the vertex group that will be controlled by the arm.
Maybe you should use the With Empty Groups mode, that is used for objects, machines, etc.
Once you've parented With Empty Groups, the mesh has now a series of vertex groups that have the same name as the bones, but none of the vertices have been assigned to any of these vertex groups, it's up to you to decide which vertices will be part of which vertex group: Just select the vertices, go into the Object Data panel > Vertex Groups, select the vertex group these vertices are supposed to be part of and click on the Assign button.
For the 2 kind of "hip" bones, that are supposed to bend the body (?), you could select the body vertices in Edit mode (don't select the head and limbs), switch to Object mode, select the armature, shift select the object, switch it to Weight Paint mode, on the top left of the 3D view click on the Paint Mask option (cube icon), shift select the 2 bones, and in the top header menu > Weights > Assign Automatic from Bones.