Well, Etrecheck thinks your internal rotational drive is failing. The Read/Write performance data also suggests this, as it is abysmally slow for even a rotational drive. This can be resolved by purchasing a fast, external, solid state drive (SSD), and installing Catalina and your third-party applications there. Then you set that drive to be the default startup drive.
Even with the 8GB of non-upgradable RAM, you simply will not believe how much faster the above Thunderbolt 3 alternative drive solution will make your iMac. That RAM suggests you will not be able to run several creative cloud applications concurrently, or in concert with Google Chrome.
You might consider the trial of Carbon Copy Cloner to clone your existing internal drive to the external drive, and then switching the startup drive in System Preferences : Startup Disk.