Full-screen flickering on external monitor (output fine but slow on X11)

I upgraded from 32 to 33 a few nights ago, and the external monitor now flashes during screen updates when on Wayland. On X11, the output appears fine, but it is terribly slow to interact with - clicking on a line in VS Code involves a 5 second wait for the cursor to appear.

I have the Lenovo Legion 5 (4600H + Gtx1650) and I’m using the nouveau drivers. On 32 these performed flawlessly.

I also booted from a live USB with 33 on it - freshly downloaded. The same problem appeared, so I think it’s quite likely a regression/new issue with something 33 has introduced.

journalctl looks uninteresting, there don’t appear to be any major warnings or issues.

I’ve also attached a GIF demonstrating the issue
61fe70e206b4fb60fe3e3c97f6e86db42a0a85f8.gif

nouveau drivers and nvidia don’t play well in the same sandbox. I first would recommend that you install the nvidia drivers then see if it still continues.

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I’ve opened an issue here External monitor flickering/white (#3811) · Issues · Mesa / mesa · GitLab

It appears that the problem is caused by the mesa-20.2 release.