Can the new Mac mini use the older version keyboard and mouse that’s plugs in?

Absolutely. When I first set up my 2018 mini I started out with the keyboard and mouse from my iMac. Since the mini helpfully comes with a few USB 3 ports you won't even need to purchase dongles to use them.

According to what (little) I could find in new Mac mini specs, the keyboard and mouse wired USB2.0 connectors

should fit correct with the newer USB3.0 ports; so that should not be an issue for you to continue use of them.

• Mac mini - Technical Specifications - Apple

(USB keyboard/mouse available in the Apple store, an optional accessory for newest Mac mini are compatible

with other USB2 devices; these use global specs & maintain backward compatibility. ~ So, this isn't a problem.)

Newer USB3 peripherals such as external drives, when attached to older spec Mac (with USB2 ports) will only

connect at the original slower specs, because there was no support engineered to higher speed, back then.

So the opposite is also somewhat true; older spec wired USB keyboard/mouse will work on newer spec Mac.

However if you should have a PC keyboard with generic key-caps for a non-Apple computer, those may not

be best if you do not know the conversion. Here is a microsoft support article for using mac keyboard w/ PC:

• Keyboard mappings using PC keyboard on a Macintosh - microsoft

https://support.microsoft.com/en-us/help/970299/keyboard-mappings-using-a-pc-keyboard-on-a-macintosh

PS: could not edit 'misleading detail' in above, as time ran out..

Fact: the Apple stores no longer offer 'Apple-brand' USB keyboard

~ that had gone missing from their inventory about two years ago.

For those who prefer a wired keyboard, helpful in troubleshooting

computer issues, without requirement for batteries to function,

there still are quality brands with apple-icon Keys for sale.

(I've kept a few 'old-stock' new Apple USB extended keyboards as spare.)