iMac Intel 21.5" EMC 2428 - Possible GPU upgrade for Catalina (Bug Sur)
Unfortunately, there's no viable GPU upgrade for the 2011 iMac (EMC 2428).
That year was the last year that particular vintage had a separate GPU &quot;card;&quot; after that (2012) they were integrated onto the logic board.
Besides the missing GPU support, there's going to be a number of missing drivers that you'll have to manually install because there are a number of discontined/deprecated components between the 2011 vintage and the 2014+ iMac (the official min. spec required).  It might make a nice project to tinker with, but if you depend on this computer, I wouldn't invest the time as it would be the equivalent of getting a classic car to use as an Über driver - you'll spend more time &quot;fixing&quot; than working.