Kinda technical question, but are side apps (deck trackers) allowed, or against EULA?
Officially? no. Unofficially? CDPR allows it (or has in the past) as long as the information obtained is available to the player. Meaning, for example, if you would be able to see the opponent's hand, it's an exploit for which you will be banned. However, if it's just tracking information, like cards played, it should be fine. Still at your own risk, though.