Encryption key nagging problem

[Aravisian]

@PerfMonk

Another possibility is I used systemd-boot on my other distros usually. Could the culprit be hidden in GRUB ??? Since Zorin use grub ??? Is it grub that ask for the passphrase firstly ???

This is possible.
Checking your BIOS settings is a suggestion, not an implication that must be where the issue is.
You can use SystemD-Boot on Zorin OS:

[HOW TO] Speed up boot using Systemd-boot

Some say that Gummiboot or Systemd-boot makes for a much faster boot time than Grub2 does. I have not tested this recently, but I can confirm it does work on Zorin OS 15 and on Zorin OS 16. Some users post on the forum looking for a way of speeding up boot time. Often, there is not a lot we can offer... aside from disabling a service here or there are recommending removing Snapd, which some users may prefer to not do. This is intended to be a linkable guide that such users may be directed to …