Very recently Roku has pushed out new firmware that blocks external control commands by default. In order for the binding to control a Roku with the new firmware, the following setting: Settings-> System-> Advanced system settings-> Control by mobile apps must be configured as Enabled or Permissive. Once this setting is corrected, the binding will work correctly again.
A PR to detect when the Roku is configured incorrectly and update documentation was opened: https://github.com/openhab/openhab-addons/pull/17925/files