I did pamac build virtualbox-ext-oracle. Rebooted.
I have my USB-devices mounted. But on the image below nothing appear there, neither when I right click on USB icon under the guest window. I also tried to add New Filter, but when click on + sign on the right it shows 'No usb devices' (I think I shouldn't do here anything at all).
Launch a virtual machine, can you not access your usb devices from the toolbar at the bottom of the window? You shouldn't have to do anything besides enabling the usb3 controller. I'm assuming you have the guest additions installed, what are you running in the VM?