I’ve outlined the steps you have to take in my 1st post. basically, add swap, add resume to loader, rebuild initramfs, selinux policies, trick systemd to ignore absent swap (it gets activated on suspend) and that’s pretty much it. then once systemctl hibernate works, switch suspend with suspend-then-resume system wide; optional, if you don’t want that (spoiler: you do want that).

first made it work on fedora (linked post in my previous reply) and then recreated it in Arch with copious help from the wiki; not much different except mkinitcpio instead of dracut. then redid it in debian first with GRUB and then replaced it with systemd-boot.

maybe do a step-by-step writeup one of these days if I find the time.