iMac 14,1 from late 2013 & Big Sur
My iMac is 14,1 from late 2013. This tells me that my iMac is not compatible with Big Sur and I can not upgrade to Big Sur - Correct?
iMac 21.5″, macOS 10.14
Correct. You can only go as far as Catalina. How to get old versions of macOS. Use only the Safari browser for that link. Bear in mind that Catalina will not run any 32-bit applications. You can determine what these are by using the free Go64 application.