how are you currently serving your react app?

railway[back, front], cloudfflare.

right but how have you configured railway to serve your frontend

this?

no, show me your deployment logs please

this?

yes, you are using serve, serve does not allow you to setup redirection rules, you would need to do the redirection via cloudflare page rules.
but may I ask why you want to redirect to www?

i think becouse here in chile all webs company work with that

okay it's your preference

yep but how can i redirect form cloudflare?

as mentioned, page rules

man you should work for the nasa xD