Can a 2018 Mac mini support dual 4k monitors at 60 Hz? I guess I need more of a personal experience answer. The specications say that a Mac mini can support dual 4k monitors, but are there any caveats to this?

I am planning to get 2 x 4k monitors and run them both at 60hz, connected through DisplayPort (I will get Thunderbolt 3 to DisplayPort adapters).
Yes, the 2018 Mac Mini can support dual 4k monitors at 60 Hz connected the way you indicate. I have this setup myself. There are no caveats.

Note: You do not need an "adapter" as such. You just need ordinary, passive cables from Thunderbolt 3 to DisplayPort.