Any recommendations on what to do with this mini-PCIe slot in my x200s?
Not sure if it matters but I have Libreboot installed. It's the slot located next to the drive slot.
Also any other upgrade recommendations while I'm at it? I have maxed out the RAM and have an SSD. I am wondering if I should upgrade the WiFi card. I don't know if there are any limitations there.
A really poor performing eGPU? You're supposed to use it for a cellular card. I'm sure you could find a 4g cellular card in mPCIe, but 5g is probably only going to be in the M.2 formfactor.
And absolutely upgrade the wifi card. They make AX wireless cards in the mPCIe formfactor for whatever reason, and they're a great upgrade over the N cards that they came with. Even AC is a huge step above.
Don't use a PCIe 4G/5G card if you care about privacy. That's giving whatever proprietary firmware is running on the baseband DMA access to your computer.