How to hibernate Debian with Secure Boot enabled and fully encrypted disk?

I'd like to be able to hibernate another one of my Debian/KDE machines because it's practical and I'd like to save some energy. I can't hibernate another one which has a swapfile and Secure Boot currently disabled. The machine runs Debian10/KDE, has Secure Boot enabled and currently doesn't have a swapfile but a swap-partition (which is larger than the RAM). The hard disk is fully encrypted. I already tried the following: * In the DE I went to Leave but unlike on my other machine there is no entry for "Hibernate". When I search for "Hibernate" the button appears but I can't right click it for more info and nothing happens when I click it. * Installing uswsusp and then running sudo s2disk. This returns:

s2disk: Could not open the snapshot device. Reason: Operation not permitted

* Installing hibernate and running sudo hibernate. This returns:

hibernate:Warning: Tuxonice binary signature file not found.  
    UdevQt: unhandlet device action "unbind"  
    UdevQt: unhandled device action "unbind"  
    UdevQt: unhandlet device action "bind"  
    UdevQt: unhandled device action "bind"

* Installing pm-utils and the executing sudo pm-hibernate. This returns nothing and nothing happens. * Running sudo systemctl hibernate.

Failed to hibernate system via logind: Sleep verb "hibernate" not supported

Searching syslog for "error" or "hibern" doesn't show anything. Is it because of security issues? I intend to change the swap-partition to a swapfile later. Hibernating with Secure Boot should be fine when the disk is fully encrypted.