Radicale is indeed excellent. Light and safe. I use it for an association!

You have to use two swaps if you already use one swap, because one will be used when the system is on, but the second will be used to set the RAM content + the 1st content into SWAP (if any), otherwise, it would fail.

Then, find the hibernation swap uuid:

sudo swapon --show
lsblk -o name,uuid

Then

# /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="resume=UUID=xxxx"

#/etc/initramfs-tools/conf.d/resume
resume=UUID=xxxx

# bash
sudo update-grub
sudo update-initramfs -k all -u

# to hibernate on lid switch
# /etc/systemd/logind.conf
HandleLidSwitch=hibernate

Then reboot :)

Note: this method works wonderfully, I use it personally. Just be aware that the hibernation swap content is not encrypted, so you’re vulnerable if your laptop is stolen while hibernated.