I liked the stacked clock on the lock screen of Samsung Galaxy S8, and changing it was also possible until recently.
My last update to Android version 9 was in March 10, 2019.
Under Settings -> Lock screen -> Clock style, you can change the style of the clock.
However, if you close the cover, you only get the same clock style and there is no way to change it.
It seems that the lastest update destroyed this feature.
My S8+ updated last night. Now the clock will not display at rest. Meaning....the display goes Black and I now have to press the button on the right side of the phone in order to see the time. Please tell me how to get back...