I have 2 Roku TVs in the house and have been using the Spectrum app on them just fine, even after their little squabble started. I ended up switching to a new Spectrum account so I could cut $60/month in fees but now I can’t log into the Spectrum app. The notice says that if you already have the app downloaded you can keep using it but when I put in my password it give me the you can’t download Spectrum app message - even though I already have it downloaded and just need to update user ID and password.
I don't have any experience with this myself other than what I've read here, but try contacting Spectrum and they should give you a code for a new channel that you can install since you already had the channel/app. I would think that you could then remove the existing channel/app and just use the new one on your Roku devices.