Nym Router v0.1.0 for the RaspberryPi 4 comes with Nym v0.12.1 bundled into each image.
See below for architecture images. If you would like to keep your OpenWRT image and install the package itself grab one of the .ipk files and install it via Opkg.
opkg install /path/to/file/nym_0.12.1-1_aarch64_XXXXXX.ipk