My PCIe Wi-Fi card is not recognized (Thinkpad x230 with Coreboot/Heads)

Since I updated my BIOS to Coreboot/Heads (I flashed a prebuild image externally), my Wi-Fi card is not recognized by lspci/iwconfig (even in the Heads recovery shell).

I tried so far:

flashing a different maximized Heads board

using a different PCIe slot (both are not recognizing it)

using a different Wi-Fi card

testing the Wi-Fi card on a different system (successfully)

tried the Wi-Fi troubleshooting guide before

lspci won’t show it (even in the Heads recovery shell)

Is there a way to activate the Wi-Fi cards in Heads? (like mentioned in the Wi-Fi troubleshooting guide)

How can I check if my PCIe slots work?