I think i remember too, that some live Iso have no suspend function, all you can do is to run or install the live usb. So i would say its normal
But i did install my gnome parallel, you then can choose your session at your login at ie. lightdm.
Beside your login name is a button to pick your session.
What was btw fun at ubuntu and i had some space, when i could have 2-3 Desktops installed and switch around as i did like to.
Its also is easy uninstalled again, if you dont like it anymore.
When i says “Access denied” i would more assume, its not loaded.
You may want do first a systemctl enable nvidia-suspend.service
When you then type systemctl start nvidia-suspend.servicethen it goes into suspend.
So the message “inactive” is logical correct, that your pc is right now not at suspend.
I did the same, and got that ugly blackscreen too, that noting as a hard reset did work anymore.
Looks like, its not the best method to send the pc into suspend.
But for this sudo systemctl suspend returned Call to Suspend failed: Access denied you may need to look for other solutions ie. the web. Seems it can be caused by other problems like here which points at comment 19 to the wiki there