Any standard half mini PCie card will work -- just make sure you don't buy the newer M.2 (NGFF) format, with which the system is incompatible.  You can find many 802.11ac cards from Intel and others. For 802.11ax, there are some half minicards that will work -- but none from Intel.  All the Intel Wifi 6 cards are M.2. For one Wifi 6 card, [URL]  
Is it possible to upgrade my Precision M6700, currently with a Centrino wireless card, to a card with 802.11ac or ax compatibility? I know some laptops have card options locked down in BIOS so they cannot be upgraded so wanted to ask before purchasing. And, if it will work, are there any recommended cards? 
M6700 802.11ac WLAN card upgrade