Hi all, Auto suspend and auto screen blank will work the 1st time after a reboot, but then stop working. Manual suspend works fine.
I guess my nvidia card (RTX 3060) is a suspect, but I'm on the latest driver.
Any suggestions on how to debug what's going on?
Switching to another driver might help, at least to identify whether this is a driver issue or not:
Cheers Zenzen, I will definitely try that at some point, but my previous experience with swapping between drivers hasn't been great, and I want to finish my current game first 
You should try to narrow the problem down by tweaking some of the power and screen settings. For example, you can prevent the system from going into sleep mode while still allowing the screen to go blank. If that works normally, at least that will tell you where the problem is more specifically.
For example:
Settings -> Privacy -> Screen.
Settings -> Power.
Older Nvidia drivers has alot of issues with suspend. Latest driver ? You installed it manually ? If yes suspend issues should be gone with the 565 releases.
Because You are using an Nvidia Card: Does Your System run in Wayland or Xorg? To check that, go the Settings>About and look there for a Line that should be called ''Window Manager'' or similar and check if there stands ''Wayland'' or ''X11''.
If there should stand Wayland, try it with switching to Xorg. To do that go to the Login Screen. There click on Your Profile so that the Password Field appears. When it is appeared, You shoud see in the bottom right Corner a Gear Icon. Click on it and choose the Option ''Zorin Desktop on Xorg''.
A much belated thanks Michel 
Now I've eventually finished my game and Xmas & New Year are behind me, I'm getting round to the update.
A couple of questions, if anyone is still watching this thread...
I've seen comments that there may be driver signing/Secure Boot issues - anything to say about that?
Also, If I go ahead with the update, what does that imply for automatic updates in the future - e.g.
You can always revert back, just make sure the driver is in the repo which worked for you. Pop OS added the 565.77 drivers 2 weeks after release. I am not sure where Zorin is at atm.
Michel was so right about the Nvidia drivers. I am glad that you got that sorted out properly. As an additional note, if you would like more power adjustment of your auto standby and suspend settings, please consider using XScreenSaver, which is the most powerful screensaver APP for Linux, IMO.
CTRL ALT T to enter terminal
Install Xscreensaver full suite...
sudo apt-get install xscreensaver xscreensaver-gl-extra xscreensaver-data-extra
Remove Gnome Screensaver...
sudo apt-get remove gnome-screensaver
To point the original lock command to Xscreensaver...
sudo ln -s /usr/bin/xscreensaver-command /usr/bin/gnome-screensaver-command
To make sure that the Xscreensaver daemon is loaded upon each start of the system, please do the following...
(1) Click on Zorin 
icon bottom of screen. Type Startup Applications Click on it, to open the menu up.
(2) Click the ADD button. Input this information into the fields and click SAVE.
(3) Now, its all initially setup and ready to go. Now all you have to do, is go back to the Zorin and type Xscreensaver, and launch it. Choose your screensaver, and what options you want.
Now, you are ready to do the stuff you really want to do with monitor power management. Click on the Advanced tab...
If you look on the right side, you can see under Display Power Management, are all the juicy settings you can adjust. Hopefully, this brings a solution where their wasn't one before.
