If you create a new container in Executor Servers perspective in Business Central with different merge mode than the default one, Keep All will still be shown in Process Configuration tab. If you try to save it, it will again show Keep All in the combo box. Note that this is probably only bug in GUI because when I start the container and get the container info using REST, I can see that the other merge mode is used.

This bug is similar to RHBPMS-4373 which has already been fixed.