Hi, I have had a similar with intermittent problems with suspend from sleep with Nvidia, although I have a fairly newish PC (2 years old) & a modern LG widescreen + older monitor. Having got fed up / frustrated with it I tried two things.
- The best solution f or me was to switch my cables to the on board AMD chip with built in graphics & cut out the Nvidia card all together. This means a switch from Display port + hdmi to hdmi + VGA but solves the problem & works really well with the power button mapped to suspend on a single press. SO suggesting the problem lies with Nvidia / drivers, although perhaps I didn’t have the right ones of enough of those installed? This is fine for me as I don’t do gaming & don’t really need the high powered graphics. It sound like you have older hardware including VGA, although maybe your onboard graphics might not be up to your needs or have enough ports perhaps?
- The other thing I tied was rolling back the 570 driver to the stable 550 drivers which worked before. However I did this via YAST by ticking a box in the Nvidia repo & this gave me some problems afterwards so I reverted to 570 and am back on my onboard card again. However someone else in another thread who had problems with an external monitor being black managed the roll back successfully via zypper and it solved their problem, so maybe that could work for you? I’ve not had the courage to try it again given the problems I had the first time. See the last few posts on this thread for the commands & how to lock it in etc. https://forums.opensuse.org/t/how-can-i-get-my-second-monitor-to-work-with-proprietary-nvidia-drivers/182602
- Hope this might help you to get it resolved.