How I make luksSuspend on standby

how I make luksSuspend on standby? because qubes not support shutdown when lid closed ? for more security

I just saw this while looking for something else; it’s very relevant to your question.

TL;DR this may work experimentally but is not officially supported; potentially viable instructions in the linked comment and the links therein.

Be aware, however, that a suspended system will always be less safe than a shut down system, see, e.g. this in the same issue.