The Thunderbolt 3 standard distinguish between two types of supplying power over the connection - either for "charging" or for "bus-powered devices".
The standard supports up to 100 watts for charging, which is it what you refer to. This is usually only supported by dedicated chargers or docking stations meant to charge laptops.
The minimum requirement of the Thunderbolt 3 standard however is that the computer must be able to provide 15 watts of power to "bus-powered devices". As far as I know, this is exactly what is supported by the Mac Mini.
If you're interested in a specific device connected to your Mac Mini, you can open up System Report where it is reported exactly how much power (in mA) that is provided to the device, and how much is available for that device.