Drop this in /var/lib/rancher/k3s/server/manifests

rancher.yaml

---
apiVersion: v1
kind: Namespace
metadata:
  name: cert-manager
---
apiVersion: v1
kind: Namespace
metadata:
  name: cattle-system
---
apiVersion: helm.cattle.io/v1
kind: HelmChart
metadata:
  namespace: kube-system
  name: cert-manager
spec:
  targetNamespace: cert-manager
  version: v1.10.2
  chart: cert-manager
  repo: https://charts.jetstack.io
  set:
    installCRDs: "true"
---
apiVersion: helm.cattle.io/v1
kind: HelmChart
metadata:
  name: rancher
  namespace: kube-system
spec:
  targetNamespace: cattle-system
  version: v2.7.0
  chart: rancher
  repo: https://releases.rancher.com/server-charts/latest
  set:
    ingress.tls.source: "letsEncrypt"
    letsEncrypt.ingress.class: "traefik"
    letsEncrypt.email: "MY-EMAIL"
    hostname: "MY-ADDRESS.sslip.io"
    antiAffinity: "required"
    replicas: 1