While creating a Machine Catalog, the following error appears:

Error:
“Unable to find valid INGRESS and EGRESS quarantine firewall rules for VPC ‘xxxxxxxxx’ in project ‘xxxxxxxx’. Please ensure you have created ‘deny all’ firewall rules with the network tag ‘citrix-provisioning-quarantine-firewall’ and proper priority.”

It is mandatory to verify this Citrix document & configure the firewall rules : https://docs.citrix.com/en-us/citrix-virtual-apps-desktops/2411/install-configure/machine-catalogs-create/create-machine-catalog-gcp.html#firewall-rules

IAM Permissions:

• The primary Citrix Service Account has been granted the Computer Admin and Service Account User roles.
• Both the primary Citrix Service Account and the Cloud Build Service Account have been granted the Computer Network User role.

Firewall Rules:

• Both the Ingress (Allow) and Egress (Deny) rules were created
• Both rules use the exact target tag: citrix-provisioning-quarantine-firewall.
• Both rules have high priority values
• All rule parameters (source, destination, ports) have been checked and found to be correct.

The issue occurs because the quarantine firewall rules were not configured with the highest priority.

GCP firewall rule priorities range from 0 to 65535, where lower values indicate higher priority. If a priority is not explicitly set, GCP assigns a default priority of 1000.
During catalog creation.

The Citrix plugin evaluates firewall rules and selects the rule with the highest priority (lowest numeric value). If multiple rules exist, the plugin may not identify the intended quarantine rule when priorities are higher or equal to the default value.

Set the priority of firewall rules to 0.
This ensures the rules are selected correctly by the Citrix provisioning plugin and resolves the catalog creation failure.

This article describes about the creation of machine catalog in GCP when using shared VPC where the machines are hosted in one project & firewall rules are applied in different project

https://docs.cloud.google.com/firewall/docs/firewalls#priority_order_for_firewall_rules