In the Operator installed RHDH, the configMap for dynamic plugins needs to have the yaml filename ending with .yaml extension. If the filename in the configMap ends with .yml none of the dynamic plugins are loaded, and there is no error/warning about this in the console.

Here's a working version of dynamic plugins cm (extension is .yaml):

data:
  dynamic-plugins.yaml: |
    includes:
      - dynamic-plugins.default.yaml
    plugins:
      - package: './dynamic-plugins/dist/backstage-plugin-catalog-backend-module-github-dynamic'
        disabled: false
        pluginConfig: {}

The same config that does not work (extension is .yml):

data:
  dynamic-plugins.yml: |
    includes:
      - dynamic-plugins.default.yaml
    plugins:
      - package: './dynamic-plugins/dist/backstage-plugin-catalog-backend-module-github-dynamic'
        disabled: false
        pluginConfig: {}

The configMap is referenced using the following config:

dynamicPluginsConfigMapName: <NAME_OF_DYAMIC_PLUGIN_CM>

Other configMaps that are referenced in the Backstage config (in application.appConfig.configMaps field) are read in (and applied) properly even if their name ends with .yml.

I'm not sure whether this is a defect or just needs doc update to mention this shortcoming/requirement. Please adjust the issue type and component accordingly.