First, I have to admit to not understanding the difference between Wallpaper and Lock Screen. That doesn't make it any easier to solve my current problem.
On my S10, I have for a long time had a family group photo showing when I first started the phone. (Is this the 'wallpaper'?). Only when I tried to use a different photo did I hit an amazing problem. After tinkering with Settings I now see (sometimes) an old photo that I took some time ago and is thoroughly unattractive, and which I don't want to display, or even keep; it alternates with one that I am happy with.
Here's the real puzzle. The photo I am happy with comes from my Gallery, but I cannot find the 'bad' photo anywhere on my phone! Except when it pops up, unwanted, from time to time. This is hair-tearing stuff. How can I stop it happening, and how can I get rid of a photo that I can't find?
There is, @Thomasalive07. You can access it in Settings > Themes. You'll be able to install themes from here. If you want to add it to your Home screen or Apps screen, you can do this by tapping on Menu in the bottom left-hand corner > Settings toggle in the top right-hand corner > Select 'Add Galaxy Themes to Home and Apps screens.