This worked for me after i borked the router.
One important step though, is that nowadays it seems like there is too much automation.
I couldn't get the tftp client to connect, until i placed a dumb switch between the router and the computer.
Google tells me its because the computer shuts down...
Just wanted to give my 2c as well.
I have an AiMesh system with a TUF AX5400 master,1x wired in switch, 2x ethernet connected rt-ac68u nodes, and i needed to connect 2x pc directly to the main router.
So i needed an extra port.
Heres what i did
Added a 1gb usb dongle
WAN->Enable usb mode:ON...