I got a Sapphire RX6600 almost a year ago, and it has always had a weird problem where occasionally the screen will flash black. I had hoped driver updates would fix it but no such luck. I think it has happened in games, but generally it only happens while web browsing, and very infrequently. The only way I have found to reliably reproduce it is to play music in Windows Media Player WITHOUT visualizations. In that case it happens roughly every 30 seconds, with a corresponding 100% GPU spike in Task Manager. Lowering refresh rate from 144hz to 120hz seemed to help, but I had done a clean driver update which set it back to 144hz and it seemed to be better, but the issue definitely still exists.
I haven't tried to overclock but when it was new I did try the automatic undervolt in Adrenalin, which failed and reverted to default tuning.
FWIW I got a new PSU when I got the card, and am using the same monitor and DP cable as I had on my previous card, which had no issues.