Posting here if someone have an idea on how to do this

Setting this env variable worked for me:

Enter your passphrase to unlock config/secrets

(set PULUMI_CONFIG_PASSPHRASE to remember):

@straight-napkin-70642 Oh ! you are right, I thought this was ONLY to unlock the secret store, but actually it WORKS for initializing stacks too. Could not find this info anywhere in the docs, maybe I missed it. Thank you.

You're welcome. Pulumi is under heavy development but it looks promising.