I changed just the disk of the notebook and installed Debian 12 on it, without any encryption and suspend works fine on kernel 6.1.0-18. Which makes me conclude that something is wrong with some patch of that Debian kernel, not allowing the disk to be decrypted with sedutil after waking up. I don't think the problem is on mainline Linux kernel because it is reported to work at least up to kernel 6.6.7-arch1-1 ( https://github.com/Drive-Trust-Alliance/sedutil/issues/90#issuecomment-1952402111 )
