Welcome to Roku Community.
It seems that you are encountering an issue with Alexa controlling your Roku device. I understand that you have tried disabling the Roku app in Alexa, however, it is still not working. Before you can use the Roku skill for Alexa, make sure your Roku device is running Roku OS 9.1 or higher. You can find the software version by visiting Settings > System > About.
For additional troubleshooting, we recommend you go to this link: How to use Amazon Alexa to control your Roku streaming device
Keep us posted on how it goes.