So I just worked through trying to make Debian/bookworm do hibernation with encrypted swap and Secure Boot. I got hibernation to a swap file setup using the resume option. Looks like the Linux kernel is fine with using a swap file from an encrypted partition, but now the requirement is apparently that the swap is signed to prevent modification.
Lockdown: resume: hibernation is restricted; see man kernel_lockdown.7
I stuck what I know here https://wiki.debian.org/Hibernation#UEFI_.2F_Secure_Boot
Going to the “Power” settings in the Dell XPS BIOS and disabling “Block Sleep (S3)” makes this promising message show up in the kernel logs:
Low-power S0 idle used by default for system suspend"
Blog of Annoying Technical Details 