My external display just started going to rainbow static and back over and over again. Didn't think to blame the update till now. Also just had my first kernel panic in about a year.
I also hadn't thought to blame the update for this until now (as I just have lost all faith in this particular model) but the timeline matches up well.
Edit: after re-reading, I think I know what you're referring to about the random static on the external display, which I've experienced over HDMI and Apple hasn't been able to debug (support case open for more than a few months now).