Kernel Panic Cure iMac 2019, Externel Monitors and Big Sur

All,

I have been kicking this around for about 7 days.

Lots of kernel panics every time my Mac goes to sleep.

My system is 2019 27" iMac, i9, AMD Radeon Pro Vega, 128GB RAM, 1TB SSD, 2 x 4K 28" External Phillips monitors connected with TB3 to DisplayPort.

~library/logs/DiagnosticReports shows lots of gpuRestarts

Apple Support suggested that this is likely bad 3rd party memory. They also stated it would not be anything to do with the external monitors or their cables. Also said might be my 3rd party WD Ex SSD

I ran Etre and Mac Diagnostics, and Rember and all came back clean.

Ran repairs on all disks. SSD was clean, but the WD Passport wouldn't repair, and showed issues so I scraped it.

I did a fresh install on the erased system SSD, and still had the problem.

Changed the TB3 to DisplayPort cables for higher quality and still had the problem.

Finally isolated that the gpuRestarts only happen in sleep.

Realised then that the issue is when iMac gets a notification in sleep mode, or emails arrive in sleep.

Changed settings in >System Preferences > Notifications

Unchecked When display is sleeping

Changed settings in >System Preferences > Energy Saver

Unchecked Enable Power Nap, Prevent computer from sleeping automatically when the display is off, wake up for network access, and start automatically after power failure

I have no been running for 48 hours without any restarts or failures, or the dreaded Restarted Because of a Problem notice.

I don't know if this is in anyway a fix all, but it has worked for me, and stopped a heap of frustrations.

I have also ordered two Moshi USB-C cables that Apple recommend for USB-C to DiplayPort. Will see if the problem is repeatable with these new cables. but at £50 each for cables. I'm expecting them to program for me too!

I will add what happens next if the cables work....