When I insert a pen drive in the USB slot of my Mac mini 2018 the Bluetooth mouse and keyboard lose connection. Anyone knows how to solve this?
I have Mojave 10.14.2 and both mouse and keyboard are Apple.
This is most likely Bluetooth interference from radio frequencies.
Your choice is probably to not use a USB or get another device.
This means that any USB 3 port, cable or USB 3 device can emit radio frequencies that may cause interference with any Bluetooth devices you using in your computer.
The issue is that USB 3.0 hard drives can emit radio frequencies that interfere with Wi-Fi and Bluetooth transmissions on the 2.4 GHz band, especially when placed near the antennas in your laptop.