On Samsung devices, there's is an option under the Accessibility menu. Then go to something like "Improve Display" (mine is in Hebrew, so that is a rough transl

On Samsung devices, there's is an option under the Accessibility menu. Then go to something like "Improve Display" (mine is in Hebrew, so that is a rough translation that might not be exact) and then "Customize Colours" (again, rough translation). Additionally, I believe that there exists an additional method to enable greyscale in Developer Options if you have that enabled.