same thing... any idea?
I think you have confused a lot of people here by talking about 'tearing', how bad is it exactly? It sounds like from your posts it is very severe, which is why I think many of the strange xorg.conf fixes, GRUB cmdline options you set are unlikely to fix your issue.
I also don't think the issue is firmware related, theoretically Debian 11 should have good Comet Lake support, on Kernel 5.10. But it is worth backporting a newer kernel to see if there is a fix.
https://www.phoronix.com/news/Intel-Com ... -Linux-Add
https://www.phoronix.com/news/Comet-Lake-Linux-5.2
You should describe in more detail the nature of the tearing and flickering, is it only when watching Netflix? Does it only happen in a web browser? How severe is it? Go into more detail about your display configuration, (Laptop screen, or an External Screen, if so, what cable?), resolution, monitor etc...
See the section here on Intel
https://wiki.debian.org/GraphicsCard
Are you sure you are using Wayland or X11? It is unclear from your post(s). Neither when properly configured should have screen tearing issues, but Wayland is little bit overweight on purpose to try to make it not a problem.