That Mac mini was End-of-Support lifed last year. Apple just did the same for the 2010 Mac Minis this month. Six years is about what you can expect for support on updates before the update certificates are no longer updated on Apple computers and other devices. The hardware is getting to the point of no longer being capable of handling the new OS functions, especially in the security area.
Thanks. Guess a new Mac Mini is in order.....bummer - my old one is doing fine.....