I had some time to play: I fetched Fedora 33 and ran it as a live USB. Then I installed darktable (dnf install) onto the USB stick, opened a RAW file (a .RAF in my case) in darktable and finally I exported it as a .JPG set to 100%.
It worked just fine.
You said that 1 minute export time is normal time on your computer. This makes me wonder about your setup:
CPU?
Motherboard?
Graphics card?
What if you remove your present darktable installation, reboot, and then install darktable again?
I am sure that there is a simple explanation/remedy to all this; the problem is just to find the culprit…
Have fun!
Claes in Lund, Sweden