Power settings and lock screen

Hi,

Hoping someone can help me. I have a policy that is configured to lock the screen after 5 minutes but not go into power saving mode for 15. I'd like the screen to lock but remain on with a specific lock screen image. The problem I face is that when my device locks after minutes, the screen goes black. I have tried numerous fixes and followed guidance but I cannot seem to get the right configuration.

Please can someone help and advise where I am going wrong. I am happy to provide any configuration evidence at request.

Regards
Ben