The Mac Mini is using full desktop components, not NUC laptop components. That's why it supports 4 times as much RAM, Thunderbolt 3, and a 65 watt CPU compared to the 25 watt NUCs.
Depends on which model. I got one earlier this year with a 7th gen core i5 processor: NUC7i5BNH with a i5-7260U, 2 cores, 4 threads, 15W TDP. Now you can get them with 8th gen core processors like these (among others):
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