Will Apple include Mac mini 2014 late in his next OS upgrade after Catalina?
If I take the reference of the following screenshot for all old models of Apple, your macMini should last for a couple of years more. After 8 years also, late 2012 still supports Catalina. 



In nutshell, if there are no any major hardware changes in upcoming macOS, I guess your 2014 will definitely support the next version of macOS.