Funny enough, I recently purchased one of the latest TP-Link Archer 5400x (AX73) routers. Ended up not needing it, so I opened it up and connected via UART.
Once you log in it appears to be running a version of OpenWRT, although they don't specify that on their website.
Once you log in it appears to be running a version of OpenWRT, although they don't specify that on their website.