it might be interesting to use unused or extra wifi cards to support this. My pc motherboard has both wifi and ethernet and I only use the ethernet. That card does absolutely nothing at all.

That's not quite accurate, I don't think.

I've definitely used STA and AP modes concurrently on my Windows laptop with the operating system's built-in internet connection sharing function to help troubleshoot a problem in the field.

That was around a decade ago. It didn't take any extra effort on my part; I just told it to do the thing, and then it did that thing.

Researched this for a bit: there is some hardware for PCI supporting it, but Windows 10/11 not, and Linux is still work in progress, so no real support on OS level, only for some iOS/Android devices.

Afaik the hardware supports it for a while now, but there is no firmware to expose the functionality.