I have found the issue, the serviceaccounttemplate parameter was wrong, plus, you have to set up the crossplane's service account appropriately, apperently, EKS requires a specific annotation for the service account, according to this documentation , which in my case had to be added via the crossplane helm & terraform since thats how I installed it, like this:

resource "helm_release" "crossplane" {
  name       = "crossplane"
  repository = "https://charts.crossplane.io/stable"
  namespace  = var.crossplane_config.namespace
  create_namespace = true
  chart      = "crossplane"
  version    = "1.19.1"
  timeout    = "300"
  values = [<<EOF
    serviceAccount:
      name: "${var.crossplane_config.service_account_name}"
      customAnnotations:
        "eks.amazonaws.com/role-arn": "${aws_iam_role.crossplane_oidc_role.arn}"
    EOF
  ]
}

Additionally, notice the service account name specification, I've made sure it matches the DeploymentRuntimeConfig Crossplane resource:

apiVersion: pkg.crossplane.io/v1beta1
kind: DeploymentRuntimeConfig
metadata:
  name: podidentity-drc
spec:
  serviceAccountTemplate:
    metadata:
      name: crossplane
---
apiVersion: pkg.crossplane.io/v1beta1
kind: DeploymentRuntimeConfig
metadata:
  name: default
spec:
  serviceAccountTemplate:
    metadata:
      name: crossplane
---
apiVersion: pkg.crossplane.io/v1
kind: Provider
metadata:
  name: provider-aws
spec:
  package: xpkg.upbound.io/upbound/provider-aws-s3:v1
  runtimeConfigRef:
    name: podidentity-drc