I have the same issue. The fan works at full speed but if you turn it down, it stops after a few minutes and you need to restart the car to get it working again at full speed. I have purchased a second-hand resistor on EBAY for £30.00 Hopefully this is the correct one as I haven't fitted it yet but I believe the part number is 2776100A26.
I found on Ebay under - NISSAN QASHQAI J11 1.5 dCi Interior Heater Resistor 2776100A26 81kw 2019. The older model J10 uses a completely different one.
I suppose the problem with this is if you are troubleshooting an issue you are not sure if you are using a working component - but it's worth a try. I have attached a photo of the old one in place. To access it you remove the glove box and you will find it at the back on the RHS. I assume you remove the two connected wires, remove the one screw and the clip, then do the same in reverse. If anyone else has replaced one, I would love to hear about your experience to avoid any issues. The placement looks awkward so I hope it's easy enough to get out. Hopefully, this helps someone else as seems a common problem. Disappointed to get it myself as the car has only done 15k miles.
QASHQAI DIESEL HATCHBACK - 1.6 dCi N-Connecta 5dr