Hello legrandtimonier,
Welcome to GCC!
If TCP:22 is already allowed in your firewall with type Ingress, then there is no issue with GCP Firewall but your next step is also to configure your firewall to allow access through Identity-Aware Proxy (IAP).
If you need to set up your instance with Identity-Aware Proxy (IAP), you may refer to this document Setting up IAP for Compute Engine. But if you already set up your instance, you just need to enable IAP Enabling IAP for Compute Engine.