Not sure about Debian, but on Arch Linux, hibernation with FDE works perfectly on my Framework laptop. It took a little to setup; I use a swapfile for my swap. And it exists on my encrypted drive. You know your use case best,I found for my usecase, a separate swap partition (to say nothing about two separate ones) was restrictive and unnecessary. A swapfile works well and lives on an encrypted drive. No need to tinker too much beyond that. Check out the Arch wiki, it might not align 100% with Debian but those wikis are super informative and can teach you how the process works so you can apply to Debian.
Not sure about Debian, but on Arch Linux, hibernation with FDE works perfectly on my Framework laptop. It took a little to setup; I use a swapfile for my swap. And it exists on my encrypted drive. You know your use case best,I found for my usecase, a separate swap partition (to say nothing about two separate ones) was restrictive and unnecessary. A swapfile works well and lives on an encrypted drive. No need to tinker too much beyond that. Check out the Arch wiki, it might not align 100% with Debian but those wikis are super informative and can teach you how the process works so you can apply to Debian.
https://wiki.archlinux.org/title/Dm-crypt/Swap_encryption#With_suspend-to-disk_support