The short answer is "yes." I've been running an RPi4 for several months. Here is where I would start:
- Download the 21.02-RC1 image for the RPi4. This includes LUCI and you can add packages whenever you like (unlike the snapshot images)
- Figure out how to connect to your RPi4 after flashing the image
- Download the required drivers for your usb ethernet adapter
- Configure the RPi4 with the usb ethernet dongle as the WAN and the internal ethernet adapter as the LAN
Let us know how it goes. There are also community builds you can look at that include usb adapter drivers and other packages in one image.
There are also lots of existing posts in the forum on setting us a RPi4.
https://forum.openwrt.org/t/rpi4-step-by-step-set-up-please-help/75184/8