There is an error message logged in controller manager pod that says tolerationSeconds would be ignored if effect is not NoExecute.
---

2022/10/03 15:00:40 reconciling (/v1, Kind=Service) metallb-system/controller-monitor-service
2022/10/03 15:00:40 update was successful
2022/10/03 15:00:40 reconciling (apps/v1, Kind=DaemonSet) metallb-system/speaker
2022/10/03 15:00:40 does not exist, creating (apps/v1, Kind=DaemonSet) metallb-system/speaker
1.6648092402562873e+09    INFO    controllers.MetalLB    Failed to update metallb status    {"metallb": "metallb-system/metallb", "Desired status": "Available"}
1.6648092402563276e+09    ERROR    Reconciler error    {"controller": "metallb", "controllerGroup": "metallb.io", "controllerKind": "MetalLB", "metalLB": {"name":"metallb","namespace":"metallb-system"}, "namespace": "metallb-system", "name": "metallb", "reconcileID": "e0e20b0b-c0a4-4527-8b32-8b5bb1d39460", "error": "FailedToSyncMetalLBResources: could not apply (apps/v1, Kind=DaemonSet) metallb-system/speaker: DaemonSet.apps \"speaker\" is invalid: spec.template.spec.tolerations[2].effect: Invalid value: \"NoSchedule\": effect must be 'NoExecute' when `tolerationSeconds` is set", "errorVerbose": "DaemonSet.apps \"speaker\" is invalid: spec.template.spec.tolerations[2].effect: Invalid value: \"NoSchedule\": effect must be 'NoExecute' when `tolerationSeconds` is set\ncould not apply (apps/v1, Kind=DaemonSet) metallb-system/speaker\ngithub.com/metallb/metallb-operator/controllers.(*MetalLBReconciler).syncMetalLBResources\n\t/workspace/controllers/metallb_controller.go:169\ngithub.com/metallb/metallb-operator/controllers.(*MetalLBReconciler).reconcileResource\n\t/workspace/controllers/metallb_controller.go:116\ngithub.com/metallb/metallb-operator/controllers.(*MetalLBReconciler).Reconcile\n\t/workspace/controllers/metallb_controller.go:100\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile\n\t/workspace/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:121\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler\n\t/workspace/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:320\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem\n\t/workspace/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:273\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2\n\t/workspace/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:234\nruntime.goexit\n\t/usr/lib/golang/src/runtime/asm_amd64.s:1571\nFailedToSyncMetalLBResources\ngithub.com/metallb/metallb-operator/controllers.(*MetalLBReconciler).reconcileResource\n\t/workspace/controllers/metallb_controller.go:118\ngithub.com/metallb/metallb-operator/controllers.(*MetalLBReconciler).Reconcile\n\t/workspace/controllers/metallb_controller.go:100\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile\n\t/workspace/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:121\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler\n\t/workspace/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:320\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem\n\t/workspace/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:273\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2\n\t/workspace/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:234\nruntime.goexit\n\t/usr/lib/golang/src/runtime/asm_amd64.s:1571"}
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem
    /workspace/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:273
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2
    /workspace/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:234

4.12

Always

1. Install the metallb operator
oc get csv -n metallb-system
NAME                                   DISPLAY            VERSION               REPLACES                               PHASE
metallb-operator.4.12.0-202209302306   MetalLB Operator   4.12.0-202209302306   metallb-operator.4.11.0-202209280142   Succeeded


2. Taint two master nodes and one worker node.

oc get nodes
NAME                           STATUS   ROLES                  AGE     VERSION
asood-103-v59jh-master-0       Ready    control-plane,master   3h12m   v1.24.0+8c7c967
asood-103-v59jh-master-1       Ready    control-plane,master   3h12m   v1.24.0+8c7c967
asood-103-v59jh-master-2       Ready    control-plane,master   3h12m   v1.24.0+8c7c967
asood-103-v59jh-worker-nnln2   Ready    worker                 175m    v1.24.0+8c7c967
asood-103-v59jh-worker-wrxkn   Ready    worker                 170m    v1.24.0+8c7c967

oc adm taint node asood-103-v59jh-master-1 group=infra:NoSchedule
node/asood-103-v59jh-master-1 tainted
oc adm taint node asood-103-v59jh-master-2 group=infra:NoSchedule
node/asood-103-v59jh-master-2 tainted
 
oc adm taint node asood-103-v59jh-worker-nnln2 group=infra:NoSchedule
node/asood-103-v59jh-worker-nnln2 tainted
  
3. Create a metallb CR with YAML below:-
oc get metallb metallb -n metallb-system -oyaml
apiVersion: metallb.io/v1beta1
kind: MetalLB
metadata:
  name: metallb
  namespace: metallb-system
spec:
  controllerTolerations:
  - effect: NoSchedule
    key: group
    operator: Equal
    tolerationSeconds: 10
    value: infra
  logLevel: debug
  speakerTolerations:
  - effect: NoSchedule
    key: group
    operator: Equal
    tolerationSeconds: 10
    value: infra

The controller and speakers are not created, but error is logged.

The user should should be warned about the combination of values when user is creating the CR.