[docs] Add a note about minimal required version for theme merging to…

… the guides (mui#36973)

docs/data/joy/guides/using-joy-ui-and-material-ui/using-joy-ui-and-material-ui.md

@@ -18,6 +18,11 @@ Additionally, keep these in mind when using them together:
 - Both of them use [MUI System](/system/getting-started/overview/) as their style engine, which uses React context for theming.
 - Theme scoping must be done on one of the libraries.
 
+## Prerequisite
+
+- Have `@mui/material` and `@mui/joy` installed in your project.
+- The version of both libraries must be [v5.12.0](https://github.com/mui/material-ui/releases/tag/v5.12.0) or higher.
+
 ## Set up the providers
 
 Render Material UI's `CssVarsProvider` inside Joy UI's provider and use `THEME_ID` to separate the themes from each other.

docs/data/material/guides/styled-engine/styled-engine.md

@@ -120,7 +120,7 @@ This package-swap approach is identical to the replacement of React with [Preact
 Having more than one styling libraries could introduce unnecessary complexity to your project. You should have a very good reason to do this.
 :::
 
-Material UI can coexist with other libraries that depend on emotion or styled-components. To do that, render Material UI's `ThemeProvider` as an inner provider and use the `THEME_ID` to store the theme.
+Material UI, starting from [v5.12.0](https://github.com/mui/material-ui/releases/tag/v5.12.0), can coexist with other libraries that depend on emotion or styled-components. To do that, render Material UI's `ThemeProvider` as an inner provider and use the `THEME_ID` to store the theme.
 
 ```js
 import { ThemeProvider, THEME_ID, createTheme } from '@mui/material/styles';
@@ -141,6 +141,10 @@ function App() {
 
 The theme of Material UI will be separated from the other library, so when you use APIs such as `styled`, `sx` prop, and `useTheme`, you will be able to access Material UI's theme like you normally would.
 
+### Minimum version
+
+[Theme scoping](https://github.com/mui/material-ui/pull/36664) has been added to Material UI v5.12.0, so be sure you're running at that version or higher.
+
 ### Using with [Theme UI](https://theme-ui.com/)
 
 Render Material UI's theme provider below Theme UI's provider and assign the material theme to the `THEME_ID` property.