Could post a link to one of these tutorials? Be aware that they could be about Samsung devices (or from another big player brand), which are different from stock android and on which you won’t get the same options at the same place.
For me under LOS17.1@FP2 I have these theming options in Settings→Styles and Wallpapers.
Otherwise you can also change the icon pack (long press on the home screen→Home screen settings→Icon pack).
If you would like to do some more theming, you shoud try a different launcher.
Nova for example has a large fan base. Many people here swear by Lawn Chair 2 (the project is in some kind of hibernation mode, though). Just search for yourself and see which one you would prefer: