Well your iMac and the version of Mac OS are pretty old. I would recommend checking with both Disney Plus and Paramount (+) to see if they still support Catalina. It is not unusual at all for software developers to drop support on legacy operating systems. You are very fortunate the 2013 iMac still runs, it is getting pretty old at 12 years old and is consider obsolete (meaning it cannot run current versions of Mac OS) and vintage which means parts are largely unavailable if it needs repair.
If you find that the software developers no longer support Catalina then it's probably time to begin shopping for your new Mac. However, get back to us and let us know what you find out. If they do support Catalina then we can have you post an EtreCheck report of the computer to see if there are obvious issues you don't know about or have missed.