I forced latest generic Intel graphics driver to install. Also I updated drivers for discrete gpu (AMD Radeon 8750m). Aaand... it changed nothing. Then I changed timing to CVT-RB (tutorial here) and at least flickering was gone. Also gradient banding is now less visible (not much). Still not ideal, but maybe this information will help someone.
Thank you for the information, I am sure this will help other community members.