Hello,
Are you able to access Starlink dish over default gateway address 100.64.0.1, when it is connected directly to PC?
Have you tried to give PC's interface a static IP from 192.168.100.c subnet and access the dish?
What address does RUT240 WAN interface receive, when it is connected to Starlink?
Could you try address given as default IPv4 gateway for RUT240 from Status -> Routes -> General routes section assigned to WAN network?
Best regards,