Most subscriptions paid through Roku are only valid on Roku devices. It was probably stated in the fine print that no one ever reads. For some services, you can try to log in on the service's website (e.g., https://www.paramountplus.com/) and try signing in with the email address used on your Roku device. Use the "forgot password" option and they may send you an email allowing you to establish a password. If they do, you'll have an email address and password that you can use anywhere. If not, you can either cancel your subscription through Roku and subscribe directly with the provider or connect a Roku device to your TV.
In general, most here would recommend not subscribing through third parties like Roku, Amazon, Apple, etc. to avoid such problems.
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