Hello all,
Sorry my English,
I have HP elitebook 840 G3 with i7-6500, 24 gb 2133 mhz ram 500 gb 850 evo M.2 ssd drive, dw1820a wifi-bt, latest BIOS.
I installed Catalina without problem (first disabled wifi in bios). I used @Hervé trick for enable the wifi. I didnt install any extra...