Does connecting a different device to the WAN port of the RUT240 work as intended? More so, when connecting the Starlink, if you go to the RUT240 WebUI → Network → Ports section, are you able to see whether the interface shows that anything is connected?
Sounds like a faulty port to me, but before we jump to conclusions, kindly try the Bootloader menu to see if the issue persists: Bootloader menu - Teltonika Networks Wiki
If the issue persists even after doing the process above, I’d strongly suggest reaching out to your distributor from whom you’ve bought the device and ask for a replacement/repair.