can i upgrade to catalina on an imac from 2007 with Yosemite?

No. Catalina requires a Mac from 2012 or later. The last compatible version with a 2007 iMac is El Capitan. See How to upgrade to OS X El Capitan - Apple Support.

No you need an iMac that supports Metal. That functionality did not become available in iMacs until 2012. No you cannot upgrade either. If you need Catalina it’s time to buy a new iMac.