Thanks for reaching out here in Roku Community.
As you have noticed, when you add an app to your Roku device, you’re actually adding it to your Roku account. As a result, the app will automatically be added to all Roku devices linked to your Roku account. When you remove an app, the same is true — it will be removed from all Roku devices linked to your Roku account.
You have the option to create a new Roku account and connect the chosen devices to it. By doing so, you can manage the devices separately, and any changes made to one account will only impact the Roku device that is associated with that specific account.
Hope this helps. Let us know if you have other questions or concerns.