can I upgrade the memory of My 2016 Macmini i5

Let's assume that you have a Mac mini 2014 that you bought in 2016. Then the answer would be, "no," 2014 Mac minis have non-upgradable RAM.

The year is for when a Mac model was introduced, not the date of your purchase.

Hello,

According to this:

https://support.apple.com/en-us/HT205041

there is no Mac mini 2016…

Identify, please, your Mac mini model as described here:

https://support.apple.com/en-us/HT201894#:~:text=Find%20the%20serial%20number%20printed,page%20to%20find%20your%20model.

and then use the upper reference.

There is no 2016 model Mac Mini.

To check your year model, go to the menu bar and select Apple > About This Mac.

Or have a look at > Identify your Mac mini model - Apple Support