I wonder if you've installed an application that has control over your video card fans? Check to see what apps are installed and also check your startup list; there might be a few of them you can temporarily disable to see if the fans subsequently come on.
Do you have a second PCIe slot on your motherboard? If so, try installing the RX 5700 XT video card into that second slot and check the fan operation.
Lastly, look for a motherboard BIOS update and if there is one, I would seriously consider installing it.
As Albert Einstein said, "I could have done so much more with a Big Al's Computer!".