Glad to hear Stillcolor works for you. There's this caveat on the
Stillcolor page:
"Note that while Stillcolor is 100% confirmed to remove GPU/DCP-generated temporal dithering, which is applied directly to the pixel framebuffer right before it's sent to the external/embedded display, the display panel's timing contoller (TCON) may still apply its own dithering/FRC to achieve advertised color bit depth. Whether or not Apple displays actively use TCON dithering in addition to DCP/GPU dithering is under investigation."