No, your equipment is simply too old and it will not be able to update Mac OS beyond 10.13.6. The reason why is that Mojave (10.14.x) and beyond require GPUs that have a feature Apple calls Metal. These GPUs did not become available on iMacs until the 2012 iMac's were released. Before you ask, no you cannot upgrade to a Metal GPU and no there are no work-arounds.
In the event you have a need to run Catalina, then it is time to buy a new Mac, something you may want to seriously consider as your 2009 is extremely out-of-date and has been considered obsolete by Apple for years due to a lack of parts availability. This means that if some hardware fails on it, getting a replacement part will not be likely. It also means Apple Stores will not work on it and finally it means that the applications you currently use on it cannot be updated to current versions of Mac OS which paints you into an obsolesce corner.
I also have an old Mac (2011 27" iMac) that I know needs to be updated, something I intend to do before the end of the year.