It seems my previous post, was not a solution afterall.  Probably something broke in my Ubuntu installation with all the stuff I did. This broke GNOME behavior when using "Lock". And apparently the side effect of this was that "Suspend" started working. (In a clean installed Ubuntu I can freeze my system by either using Lock or Suspend).  So I somehow fixed all my suspend issues, but I completely broke the "Lock" function.  After this --> I tried KDE Desktop and everything was working OK. Systemctl suspend was working, the lock screen was working.  So I installed Kubuntu 20.04 LTS from scratch. Kubuntu works out of the box. No need to change anything. No changes to grub, etc.  I can conclude that my issues are related to Gnome or something that Gnome uses (I also had suspend issues in Linux Mint and also in Lightdm).  I'll now mark this as a solution. It's not a solution for Ubuntu main flavor. But it's a solution for this laptop suspending in a modern Linux system. I'll try Lubuntu next. No issues at all with KDE. I just want to test a more simpler/light environment. If Lubuntu is too simple. I'll just go back to Kubntu.   
I'll try to be short. Installed Ubuntu 20.04 (new install) and when I use the "suspend" function, one of the following 2 results can happen: A) The laptop suspends (or hibernate) in 2-6 seconds. The power led goes OFF.  B) The laptop instantly turns off the display, leaving the keyboard backlight and power led ON, and fail to suspend. After a minute, sometimes it reboots itself automatically and boots ubuntu from scratch.    I don't know what to do to make the scenario A the only possible scenario when using "Suspend" (via the Suspend button, via the power button, closing the lid, or just selecting "suspend" option in Ubuntu GUI). Scenario B is a big problem because it basically crashes my PC.      Any ideas? I've already tried many things. Some are:             My laptop is a Dell Latitude 7390 with only Intel i5 8th gen only (no additional GPUs).    
Dell Latitude 7390 and Ubuntu 20.04 - "Suspend" barely works