Same problem on my MBP 15" Mid-2019 with the i9 for almost a year now. It started with flickering and ended up in a complete black screen (just a small notch on the top of the screen remains). Super mad at Apple for not fixing this for a whole year now. I found a workaround by unchecking "Automated Graphic Switching" in the Battery settings. But the Battery is insanely draining. I already resetted SMC, NVRAM/PRAM, Secure Boot, created a temp user, wiped all partitions, reinstalled Catalina, updated back to Big Sur, Apple System Diagnostics (shows no problem with the system), changed cursor size, deactivated True Tone / Night Shift, updated to Monterey beta, checked connector-type properties of the iGPU using IORegistryExplorer, used gfxCardStatus and much more...