Honestly, I find hibernate way more useful than sleep/suspend so I put some effort into getting mine to hibernate last night.
I added an extra (unencrypted) swap on /dev/mmcblk1p1 just to get encryption and lvm out of the picture as a test, set that up as the resume target in the kernel cmdline.
One thing we have to fix is systemd flat out refuses to even try. It says Failed to hibernate system via logind: Sleep verb "hibernate" not supported if you do systemctl hibernate.
So I tried to do it via sysfs like it says in the Linux kernel docs: Debugging hibernation and suspend — The Linux Kernel documentation
doing echo disk | sudo tee /sys/power leaves the machine unresponsive, powered on with a black screen. Maybe there’s something useful on the serial console, but I haven’t opened it to hook one up to check.
Trying the various pm_test modes, It gets past freezer and devices, but platform, processor, or core will leave it with a blank screen needing a reset.