How do I use the builtin function calls in Argo workflows expressions?

Question

I have the following Workflow YAML file:

---
apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: repro-expression-broken-
spec:
  entrypoint: repro-expressions
  ttlStrategy:
    secondsAfterCompletion: 3600
    secondsAfterSuccess: 3600
    secondsAfterFailure: 86400 # Keep workflows which fail for 1 day so that they can be investigated
  templates:
  - name: repro-expressions-main
    steps:
    - - name: reserve-release
        template: repro-expressions
  - name: repro-expressions
    inputs:
      parameters:
      - name: abc
        value: "{{=now() - duration(1h)}}"
    script:
      image: "alpine"
      command: [ash]
      source: |
        echo "test expression 1: {{=now()}}"
        echo "test expression 2: {{=2+2}}"
        echo "test expression 3: {{=split('apple,orange,grape', ',')}}"
        echo "test expression 4: {{=[max(5,7),9]}}"
        echo "test expression 5: {{=[1,3,5]}}"
        echo "test expression 6: {{='this is a string'}}"
        echo "test input expression: {{inputs.parameters.abc}}"

Submitting this workflow (argo v3.4.13) generates the following output in the logs:

repro-expression-broken-qrxzs: test expression 1: {{=now()}}
repro-expression-broken-qrxzs: test expression 2: 4
repro-expression-broken-qrxzs: test expression 3: {{=split('apple,orange,grape', ',')}}
repro-expression-broken-qrxzs: test expression 4: {{=[max(5,7),9]}}
repro-expression-broken-qrxzs: test expression 5: [1 3 5]
repro-expression-broken-qrxzs: test expression 6: this is a string
repro-expression-broken-qrxzs: test input expression: {{=now() - duration(1h)}}
repro-expression-broken-qrxzs: time="2023-11-23T10:21:33.612Z" level=info msg="sub-process exited" argo=true error="<nil>"

All the expressions that have function calls have failed to resolve to a value. Why is this?