I have just installed my Pi 5 in this case and the fan is on full all the time using just sd card or with NVME. I installed the scripts from the manual but no /etc/argon folder if that is relevant.
Any way of making the fan stop? Should I just return it for a refund?
With this case the fan should connected directly with the RPi5 pcb. If there is a fan control working or not, massively depends on your chosen distribution. The argonneo5.sh installs no daemon for that, to provide an interface is the task of a recent kernel. Some distributions let you set the thresholds via dtparam, others need an additional daemon for that…
To temporary shutdown the fan, you can try this command: echo "0" | sudo tee /sys/class/thermal/cooling_device0/cur_state