Syntax errors declaring conditional variables inside YAML jobs - yaml

Question

Trying to edit a function YAML file to include some conditional variables, but whatever I try the file won't seem to run in the pipeline.
The desired variable is an array, which I've tried declaring like this:
jobs:
- deployment: Databases
displayName: Deploy Databases in ${{ parameters.stage }}
environment: '${{ parameters.stage }}.${{ parameters.serverName }}'
timeoutInMinutes: 2880
variables:
${{ if eq(parameters.MyParam, True) }}:
MyArray: [ 'Bar' ]
${{ if ne(parameters.MyParam, True) }}:
MyArray: [ 'Foo' ]
stages: [ YAML continues ]
But when trying to run the pipeline, I get the error:
A sequence was not expected
I've tried declaring it as a simple string variable instead, but that just gives a different error:
variables:
${{ if eq(parameters.MyParam, True) }}:
MyArray: 'Bar'
${{ if ne(parameters.MyParam, True) }}:
MyArray: 'Foo'
Expected a sequence or mapping. Actual value '$(MyArray)'
Trying this syntax:
variables:
${{ if eq(parameters.MyParam, True) }}:
- name: MyArray
value: 'Foo'
${{ if ne(parameters.MyParam, True) }}:
- name: MyArray
value: 'Bar'
Yields the error:
[path] (Line: 9, Col: 5): Expected a mapping
[path]: Object reference not set to an instance of an object.
Trying this:
variables:
- name: MyArray
${{ if eq(parameters.myParam, True) }}:
value: 'Foo'
${{ if ne(parameters.myParam, True) }}:
value: 'Bar'
Gets me the same errors as my initial attempts.
I've also tried simply declaring a variable without the conditional and that also gives the same original errors. What am I doing wrong here?