Using the physical serial port on a BSFrance LoRa32u4? I can use the serial-over-USB channel by simply using Serial in my code.

The LoRa32u4 has an RXD1 and TXD1 pair on pins 20/21 (Arduino 0/1).  


https://docs.bsfrance.fr/documentation/11296_LORA32U4/LoRa32u4_pinout_diagram.pdf

How do I configure and use this serial port (for receiving NMEA GPS)?
[ATmega32U4-based boards use] Serial1 to communicate via TTL (5V) serial on pins 0 (RX) and 1 (TX). Serial is reserved for USB CDC communication. For more information, refer to the Leonardo getting started page and hardware page.