The wifi card is plugged in to the motherboard. Cheesegrater Mac Pros were notorious for having poor wifi reception because of the metal casing. I have a MacPro5,1 (mid-2012) into which I replaced the wifi card with a newer one but aware of the problem, I did not connect it to the internal wifi. Instead, I had it connected to an Apple AirPort Extreme configured as a network extender and the setup worked perfectly. If you are close enough to your internet modem, you could just connect it with a cable. I also upgraded the graphics card to metal which enabled it to run the current system—Mojave, if I remember right. And I hope you have dainty hands because it’s a challenge installing the WiFi-Bluetooth card onto the motherboard.
It worked well for me until the Mac mini came out in 2018 and I simply moved all four hard drives and two SSDs into external cases to the Mac mini. I think it had 32 gibibytes, if not 64, of RAM. It also has two optical drives. Yes, it was a mighty production machine, and nothing wrong with it except for the promise of running the more current system which is vital to my work.
I’m just waiting to send it, along with the (still working) 30" Apple Cinema Display, to an Apple Store or service provider for recycling. If you are close to my location, it’s free to anyone who can use it. I’m in the Silicon Valley area, Mountain View—you know, where Google is headquartered.