To add a usb storage support on openwrt we need to install a few packages.
Namely block-mount, e2fsprogs, kmod-usb-storage-uas, kmod-usb3 and kmod-fs-ext4.

We can either install it using LuCI or via CLI.

# run opkg update to download the package repository
opkg update

# install the need packages using only 1 line
opkg install block-mount e2fsprogs kmod-usb-storage-uas kmod-usb3 kmod-fs-ext4

Unplug then plug again the usb device if it is still not yet detected then you should be ready to go.