Open editor and preview pane in split view all the time

// ./sanity/components/auto-preivew-pane.component.tsx

import { useEffect } from "react"
import { usePaneRouter } from "sanity/desk"

export const AutoPreviewPane = () => {
  const {
    setView,
    duplicateCurrent,
    groupIndex,
    hasGroupSiblings,
    routerPanesState,
  } = usePaneRouter()

  useEffect(() => {
    // Check if "preview" is active
    const isPreviewActive = routerPanesState.some((group) =>
      group.some((pane) => pane.params?.view === "preview")
    )

    if (!isPreviewActive) {
      if (hasGroupSiblings) {
        if (groupIndex === 1) {
          setView("preview")
        }
      } else {
        duplicateCurrent()
      }
    }
    // Ignoring this because adding deps causes lots of loops
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [])

  return null
}

// ./sanity/schemas/article.document.tsx

import { AutoPreviewPane } from "../components/auto-preview-pane.component"


export const article = defineType({
  type: "document",
  name: "article",
  title: "Article",
  fields: [
    defineField({
      type: "string",
      name: "title",
    }),
    defineField({
      type:"string",
      name:"hiddenPreviewField",
      components: {
        field: AutoPreviewPane,
      },
    })
  ],
})