To answer my own question, a Wifi 6 card works fine. I put an AX210-based Wifi 6E card in my y500 (after doing the bios mod), and it works great, as does the card's bluetooth capability ... I don't have a 6ghz capable router to test with, but since 2.4 and 5 work OK, I'd assume 6 would too. The particular card I got is this: https://www.amazon.com/gp/product/B09CDFV2CL/. I had to download drivers directly from Intel, Windows did not already have them (in fact, neither did windows update). I had to dig out an Ethernet cable, I recommend pre-downloading if you want to avoid that.
As much as I love Lenovo's build quality, this will be my last Lenovo laptop. I did a little more research and it appears that they're still doing whitelists to this day ... and well, that's total BS. If it weren't for the people who put all the hard work into figuring this out, I'd be stuck either using a USB dongle or getting a new laptop. Thanks, everyone!