Similar issue. Early versions of Ventura had a screen flicker issue for external monitors connected through a dock, but this was resolved after about the second update. Sonoma seems to have picked up where this left off. Two monitors connected, one through HDMI directly through an adaptor to a thunderbolt port, the second through a dock (also connected through a thunderbolt port) and then to a Display port. Display port monitor flickers on about a 1 minute cycle whereas the HDMI display is stable. Changing refresh rates makes no difference but bypassing the dock seems to correct the problem. Checked the colour sync directory and have about 100 duplicate colour profiles, but can't delete any as suggested by other users (no ~/library/ColorSync directory). The dock is very useful as it runs my peripherals and supplies power. Seems this issue is not uncommon.