You want to prevent users from accidentally deleting a Shared VPC host project.

Enable the compute.restrictXpnProjectLienRemoval organization-level policy constraint:

This constraint prevents users from removing liens from Shared VPC host projects.

By enabling this constraint, you ensure that the Shared VPC host project cannot be accidentally deleted, as liens prevent deletion without proper authorization.

Apply this constraint via the Google Cloud Console or using the gcloud command-line tool.