I have been using arduino uno/nano clones for a long time that work with ch340.
After an update, my boards were not detected in the arduino ide.
After some research, I installed the AUR package ch34x-dkms-git which solved the problem for other people.
The installation ends without error message for my current kernel but there is no change on the situation in the ide.
The module does not start with the system, I have to modprobe it at each start.
sudo dmesg | grep ch34x give me
[ 160.025005] usbcore: registered new interface driver ch34x [ 160.025031] usbserial: USB Serial support registered for ch34x [ 232.480134] usbserial: USB Serial deregistering driver ch34x [ 232.480175] usbcore: deregistering interface driver ch34x [ 467.878692] usbcore: registered new interface driver ch34x [ 467.878706] usbserial: USB Serial support registered for ch34x
Thank you in advance.