fix: unsynchronized useSyncExternalStore snapshots with server (#3830)

.changeset/thirty-beans-dress.md

@@ -0,0 +1,5 @@
+---
+"mobx-react-lite": patch
+---
+
+fix #3826: components make two renders because of the different state of the snapshots

packages/mobx-react-lite/src/useObserver.ts

@@ -5,9 +5,6 @@ import { isUsingStaticRendering } from "./staticRendering"
 import { observerFinalizationRegistry } from "./utils/observerFinalizationRegistry"
 import { useSyncExternalStore } from "use-sync-external-store/shim"
 
-// Required by SSR when hydrating #3669
-const getServerSnapshot = () => {}
-
 // Do not store `admRef` (even as part of a closure!) on this object,
 // otherwise it will prevent GC and therefore reaction disposal via FinalizationRegistry.
 type ObserverAdministration = {
@@ -98,7 +95,7 @@ export function useObserver<T>(render: () => T, baseComponentName: string = "obs
         // Both of these must be stable, otherwise it would keep resubscribing every render.
         adm.subscribe,
         adm.getSnapshot,
-        getServerSnapshot
+        adm.getSnapshot
     )
 
     // render the original component, but have the