Engineering samples with part number ATMEGA4809-MFRES are mounted on revision 4 of ATmega4809 Xplained Pro.
Revision 4 has a new PCB that fixes the SPI MISO/MOSI issue in revision 3.
Revision 4 does not have the header footprints for external 3.3V and 5.0V supply to the mikroBUS socket.
Instead of the crystal documented in Crystals, the 32.768 kHz crystal on ATmega4809 Xplained Pro revision 4 is a Kyocera Corporation ST3215SB32768E0HPWBB 9 pF crystal. This crystal configuration is not optimally matched and has a capacitance mismatch that causes the oscillation frequency to be off by ~30 ppm.
This revision of the kit has an ATECC508A mounted on the CryptoAuthentication footprint.