Made some progress, but board is not working yet. My board is not a genuine Arduino Pro Mini but a SAMD21 mini. I presume that this is a clone with the same form-factor and wired the RFM95W board to the SAMD21 like on this page. 
I use this pin mapping:
const lmic_pinmap lmic_pins = {
.nss = 6, // chip select on SAMD21 mini
.rxtx = LMIC_UNUSED_PIN,
.rst = 5, // reset pin
.dio = {2, 3, 4}, // DI0, DI1, DI2
};
I updated my Arduino IDE: Arduino SAMD boards from v 1.8.8. to v 1.8.10; installed an Arduino USB driver (that just popped up during the update process) and updated the library MCCI Lorawan LMIC from v 3.2.0 to v 3.3.0
When I compile my code it says my board is not supported (I choose Arduino Zero (Native USB port), and I should use Explicit Pin mapping (which I do in the code). Uploading goes well, but the Serial Monitor does not appear when I request for it via the Tools menu. In the code I put // just before the
While Serial command, like this:
// while (!Serial); // wait for Serial to be initialized
So the program will not wait for this port to be ready. When I physically disconnect my board from the usb port it suddenly does appear, but with no output at all. So… I guess something is wrong in my IDE or code.