I have a similar issue. I have a Paramount+ account that I want to log into with the stand alone app, but because I used a promo offer and got a Paramount+ account on Roku I can not sign in to my stand alone Paramount+ account on the stand alone app. It keeps saying that "You already signed up on The Roku Channel, but to take full advantage of your Paramount+ subscription, create an account so you can:". Then I can only create an account not log in.
I tried to follow the steps you listed but I am not able to remove the Paramount+ app.
