Lock Screen clock

Arhh you mean Always On Display Clock. Always On, is a feature on many Android phones with OLED screen, where the clock is visible all the time. This can be done on OLED, as only the pixels to be used to display the clock are on. iPhone's top models also have OLED screen, but unfortunately they do not have this feature yet.

You can probably download an app that can mimic the Always On function, but the downside will be that your phone is not locked while showing the clock in the app.

There is already a clock on the lock screen.

Unfortunately, it is not possible to install a new clock on the lock screen.