I've been using my TCL Roku TV for years with the remote and the app on my phone.
I just had a moment of being totally fed up about them pushing substitutions and the app having ads.
I did a quick search to see if I could download load a APK or offline full version....
Then I found out whatever ap I've been using is NOT official and NOT from Roku or TCL. I went into ap info and it all read as "unknown"
I'm a pretty tech savvy guy I laugh at people who fall for these dumb scams- the ol' "you have a virus pop up click here to fix your computer. " Im 29 I feel so dumb. I've been using basically spyware on my phone for years.. fake apps asking for payment information is crazy ! Be careful out there.. watching TV. Lol
At least you realized it. You can also take some comfort in knowing not all these 3rd party unofficial apps are a scam. Some are developed as projects in an effort to provide a feature the developer sees as lacking in the official version.
However, I haven't really come across one recently that performs any better than the official Roku mobile app. (and the official mobile app doesn't have pop-up ads , so there is that also.)
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The official Roku app info can be found in the Roku Support pages. (Knowledge base)
https://support.roku.com/article/217288467 (How to install the Roku mobile app)