This is a Remix from my normal S10 case (Thing ID 3563232) with a Witcher emblem stanced into the back of it.
Holds on very snug and good on my S10.
Don't print it with hard / briddle Materials, those will pretty surely break when trying to put the phone in.
EDIT: V2. Edited the Witcher Head shape a bit, cutout looks better expecially in the mouth area now due to more holes that are all the way through. Could possibly become harder to print in the teeth area though.
Set support Density (I did it in Cura) to 5% and support type to ZigZag, that way you'll get a nice little wall you can easily rip out under the ends that go over the phone's front side.
I used Anycubic's own TPU Filament (which came out just perfect), but you could use any other flexible filament I suppose, probably non TPU aswell.