Where do I find modern WiFi 6 routers that generate low EMF radiation?

AFAIK that isn't something vendors aim for or market. One could however log into the WiFi and adjust the RF settings of most devices and lower the output power to the point where it still works for their needs if are are factoring in RF frequency EMF. e.g. try the lowest power setting and see if devices can still operate in the desired locations

If in terms of EMF you meant the lines of flux and spurious emissions leaked from the power supply then I suppose one could put the WiFi and power supply in a metal container that has holes for the antenna's to still be connected. In that case I would look for one that has detachable antennas and aftermarket external free-standing antennas. Most consumer WiFi are in plastic cases and offer no shielding into or out of the device. Most if not all of them have low quality power supplies.

If your WiFi has a standard barrel/coaxial connector for DC input then I suppose you could find one of the more expensive linear power supplies used for HAM radio that have low ripple voltage and low EMF leakage. Just ensure polarity, current capability and voltage matches the requirement of the WiFi device.

Out of curiosity what is the end goal or problem you are trying to solve? Proximity to medical gear?