Post #2658: 
Michael_Knubben:
It also makes deselecting by clicking outside the object stop functioning
Replace the code with:
bpy.ops.view3d.select(deselect_all=True)
Michael_Knubben:
Is there a way to make it so holding lmb in place makes the dropdown show up, but dragging lets me box or lasso select (depending on selected tool)?
Yes, add a Stack Key with the same keymap ( Object Mode ), same hotkey ( LMB ), Click Drag hotkey mode and this code in Command tab:
tool = C.workspace.tools.from_space_view3d_mode(C.mode); bpy.ops.view3d.select_lasso('INVOKE_DEFAULT', True) if tool and tool.idname == "builtin.select_lasso" else bpy.ops.view3d.select_box('INVOKE_DEFAULT', True, wait_for_input=False)