imac 21.5 late 2011 with i5 3.3 Ghz, 12 GB memory, Nvidia Quadro K2000M 2 Gb graphics card, will Catalina 10.15.3 update itself with future versions of the operating system?
Not completely true, there is a lively group here keeping these specific iMacs up to date with hardware and software mods like the TS with his Quadro card. This GPU is Metal capable and can run the latest OS with minor software tweaks
On topic; I would turn off automatic updates and just keep checking in the known threads here if it is without a hassle prior to updating to any newer version