1: I have used the Always on Screen, always on with my S8, family members S9, and on my S10. It DOES NOT severely drain the battery, it is designed to be "always on", hence the name... To tap the screen to see the info displayed defeats the entire purpose. The things that I want to see when glancing over at my phone are: the time, temperature, and battery level and notifications, if I had to tap the screen all the time to see these it would drive me crazy (OK, crazier). The "AOD" moves slightly to prevent burn in.
2: Try Edge Lighting Fix for all apps by zunderstruck on the play store:
https://play.google.com/store/apps/details?id=fr.zunder.edgelightingfixforallappsv2&hl=en
3: Try Holey Light by Chainfire on the play store:
https://play.google.com/store/apps/details?id=eu.chainfire.holeylight&hl=en
4: Just as it says, one is with sound and the other is not.
Battery usage on these: Holey Light for the last week used 3.6% of the battery, the other doesn't even show up.
I have nothing to do with these apps, just stating what works for me, your mileage may vary...