The Redpine Signals RS9116 supports Bluetooth 5.0 and the FOSS drivers in the Librem 5 are provided by Redpine Signals, so in theory Bluetooth 5.0 should work, but only Bluetooth 4 has been tested and the Librem 5 schematic only mentions Bluetooth 4.1.
I added this question to the Librem 5 FAQ.