No sleep whatsoever

I'm new to Linux and I'm looking for my Linux daily driver. Ubuntu Mate seems to suit my needs so far except that it does not go to suspend mode when it should. I've set timings for the system and monitor but only monitor goes to sleep.
From the Windows experience I suspect that It may be something to do with the drivers.
Motherboard: Gigabyte B450 Gaming X
CPU: Ryzen 3600X
Ubuntu is installed on SSD connected via SATA to USB adapter. Maybe that's causing the problem!?
No other hardware than internal storage disks.
Thanks.

Hi Oliver,

Does monitor go to sleep or screensaver start?
But any way, please check Screensaver settings in Control Center because “Put computer to sleep when inactive for” begins to count time since Screensaver is started.

DeepinScreenshot_select-area_20211203105654

Hey snow, wow, this is something I had no clue while testing various distros and having the same problem. First thought on Linux screensavers was "why is this still present nowadays?", and I disabled it.
Ok, so, the sleep countdown starts when the screensaver kicks in!?
Thanks.