Because everytime I go into the Pureboot setting and change the Boot option to USB option and I select Ventoy USB drive, it always fails to boot into the USB.
PureBoot/Heads are able to boot ELF, Multiboot kernels or Linux kernels (via kexec). Ventoy is not any of those things - it is only bootable via BIOS or EFI (comparable to booting Windows from PureBoot/Heads’ perspective).
While we would like to enable PureBoot and Heads to boot more OSes, in the case of Ventoy, PureBoot itself can do what Ventoy does. You can copy detach-signed ISOs to a flash drive, and PureBoot will ask which you’d like to boot.
A key limitation though is that PureBoot/Heads will only boot detach-signed ISOs currently. I believe Ventoy does not check signatures and does not care if they are signed. You can sign them yourself with the GPG key used in Heads if the distribution does not provide signatures of this type, or if their key isn’t included in Heads.
I think it is worthwhile to enable booting unsigned ISOs as well, though I can’t offer an ETA for that work. (PRs welcome )