20.04 LTS - 21.04 Standby / Hibernate does not work

Hi there,

years over years Standby and Hibernate worked well.
I believe sometimes in 20.04 with one update it was killed. Don't know witch one was it exactly.
So days with try and error are going in, I'm not able to fix it.
Million hours of reading hints on the internet won't help to keep Standby/Hibernate to work again.
The only thing I worked out was, if nouveau driver was use, no chance for hibernate. I used different graphic cards on different desktop-PCs
I've tried different nvidia-drivers and different kernels.
So my problem is I have to use Hibernat every day on two PCs.
And every day several times Standby. These features are required for me.

First used on:
Dell T3500 with GForce GTX 750 Ti with Nvidia 390.144 and 5.4.0-80-generic x86_64 and 20.04.2 LTS 64-bit 8 GB and a swapfile with 8.8 GB

Second one:
Dell T3600 with Quadro 600 with Nvidia 390.144 and 5.11.0-25-generic x86_64 and 21.04 64-bit 16 GB and a swapfile with 16.11 GB newly installed today

So what's happening:
21.04: Hibernate
sudo systemctl hibernate
Screen goes black for a second, then last screen from booting is displayed. (Ubuntu Boot Logo with dots, do nothing)
No writing to disk(swapspace), no Power down. Keyboard no function.
Reboot after pressing power until power-down.

21.04 Standby
sudo systemctl suspend
Screen goes off. Power goes off.
At power-on screen goes on, last Boot Logo is on screen, nothing happens. No strg/ctrl+alt+F1
Reboot after pressing power until power-down.

20.04.2 Hibernate
Resume button not working anymore
sudo systemctl hibernate
Not working, nothing happens

20.04.2 Standby
Standby button not working anymore
sudo system suspend
Not working, nothing happens

I'm not sure what was going wrong last time.
So any help is welcome to find out to solve this.

THX Frank

Problems with 20.04 LTS solved by Backup to older Kernel 5.4.0-77-generic .

With new installed Ubuntu-Mate 21.04 the problem exists furthermore.