why split, you could use railway and render for both front end and back end

Sorry, I wasn't saying you should split, I wanted to say that depending on what type of apps you are more leaning into one makes a bit more sense than the other. Render with their own CDN is quite good for frontend apps. In comparison, the whole config and auto scalling/provisioning of Railway makes it easier for backend app.

Of course you can do both with both of these services.