Select the different vertices of 2 objects.
- Download https://github.com/SaitoTsutomu/DiffObj/archive/refs/heads/master.zip
- Start Blender.
- Edit menu -> Preferences
- Select the "Add-ons" tab.
- Press the "Install ...".
- Select the downloaded ZIP file and press the button "Install Add-on".
- Check the "Object: DiffObj".
- Select two objects.
- Show the sidebar and select the Edit tab.
- Push "Select Diff 2 Obj".