Try to use another fs. ZFS has no official Linux kernel support and will never have it. It’s also only advantageous for server realm usage, you’re better off with ext4 or BTRFS for desktop land usage, considering the Framework is a single-drive device.
Okay I got it to work eventually with LVM + encryption. This too failed on a me a few times, until some combination of resetting Secure Boot state did the trick. Not happy that I couldn’t predictably figure out what happened, but after rebooting nearly 50 times, I was just happy I was able to complete the installation