Imported vrm/vroid models have bone names that aren't compatible with Blender's mirrored bone editing. This will toggle the vertex group names and bone names between the two versions. This script adds a menu option for object mode "VRM Swap Bone Names".

VRMSwapBoneNames.py

bl_info = {
    "name": "VRM Swap Bone Names",
    "blender": (3, 4, 1),
    "category": "Object",
}

import bpy

class VRMSwapBoneNamesOperator(bpy.types.Operator):
    
    bl_idname = "object.vrmswapbonenames"
    bl_label = "VRM Swap Bone Names"
    bl_description ="Swap VRM style bone names to append _Left and _Right to all selected objects' vertex group names and bone names. Run this operator again to swap back to VRM style names with _L_ and _R_"
    bl_options = {'REGISTER', 'UNDO'}
    
    def execute(self, context):
        def replaceName(namedObject, mode):
            if "_L_" in namedObject.name and mode >= 0:
                namedObject.name = namedObject.name.replace("_L_","_d_")+"_Left"
                return 1
            elif "_R_" in namedObject.name and mode >= 0:
                namedObject.name = namedObject.name.replace("_R_","_d_")+"_Right"
                return 1
            elif "_d_" in namedObject.name and "_Left" in namedObject.name and mode <= 0:
                namedObject.name = namedObject.name.replace("_d_","_L_").removesuffix("_Left")
                return -1
            elif "_d_" in namedObject.name and "_Right" in namedObject.name and mode <= 0:
                namedObject.name = namedObject.name.replace("_d_","_R_").removesuffix("_Right")
                return -1
            return mode
            
        mode = 0
        for target in bpy.context.selected_objects:
            v_groups = target.vertex_groups
            for vg in v_groups:
                mode = replaceName(vg, mode)
            if target.type == 'ARMATURE':
                for b in target.data.bones:
                    mode = replaceName(b, mode)
                    
        return {'FINISHED'}
    def invoke(self, context, event):
        return self.execute(context) 

def menu_func(self, context):
    self.layout.operator(VRMSwapBoneNamesOperator.bl_idname)

def register():
    bpy.utils.register_class(VRMSwapBoneNamesOperator)
    bpy.types.VIEW3D_MT_object.append(menu_func)

def unregister():
    bpy.utils.unregister_class(VRMSwapBoneNamesOperator)
    
if __name__ == "__main__":
    register()