devilgrove You can simply verify the result by the command
log show --predicate "processID == 0" | grep Dither
If you entered the correct command, you can see such kernel log
Default   0x0         0   0  kernel: (AppleIntelICLLPGraphicsFramebuffer) [IGFB][LOG ][MODESET  ] Dither is disabled in pipe misc
if it will print out
Default   0x0         0   0  kernel: (AppleIntelICLLPGraphicsFramebuffer) [IGFB][LOG ][MODESET  ] Dither is enabled in pipe misc
the command, you entered, was incorrect.