Material-ui provides insights into resolving this issue with three different approaches.

Link to Material-ui documentation

1. Consider using the position="sticky" attribute instead of fixed, keeping in mind that sticky is not compatible with IE 11.
2. You have the option to display a second component as a workaround.
3. An alternative solution is to utilize the theme.mixins.toolbar CSS.

In my experience, I prefer implementing the second solution like so:

  return (
    <>
      <AppBar position="fixed">
        <Toolbar>{/* content */}</Toolbar>
      </AppBar>
      <Toolbar />
    </>
  );

To enhance the AppBar in MaterialUI, you can utilize a theme mixin specifically designed for it. It's important to ensure that you are using the recommended JSS setup. Here is an example of how you can implement this:

import withStyles from '@material-ui/core/styles/withStyles';
const styles = theme => ({
  appBarSpacer: theme.mixins.toolbar
});

const style = withStyles(styles)

function MyScreen ({ classes }) {
  <AppBar></AppBar>
    <div className={classes.appBarSpacer}></div>
  <Box></Box>
}

export default style(MyScreen)

By using this mixin, the div will automatically adjust its height to match that of your AppBar, creating a seamless design for your content.

<AppBar position='static'>

Implementing this code will prevent content from being hidden under the AppBar.

In my opinion, the key to a successful app setup is crucial and I have some recommendations:

import React from "react";
import ReactDOM from "react-dom";
import {
      AppBar,
      Typography,
      Box,
      CssBaseline,
      makeStyles,
      Container,
      Grid,
      Toolbar
    } from "@material-ui/core";

    const useStyles = makeStyles((theme) => ({
      content: {
        flexGrow: 1,
        height: "100vh",
        overflow: "auto"
      },
      appBarSpacer: theme.mixins.toolbar,
      title: {
        flexGrow: 1
      },
      container: {
        paddingTop: theme.spacing(4),
        paddingBottom: theme.spacing(4)
      }
    }));

    function App() {
      const classes = useStyles();
      return (
        <div className={classes.root}>
        <CssBaseline />
        <AppBar position="absolute">
        <Toolbar className={classes.toolbar}>
        <Typography
        component="h1"
        variant="h6"
        color="inherit"
        noWrap
        className={classes.title}
        >
        AppBar
        </Typography>
        </Toolbar>
        </AppBar>
        <main className={classes.content}>
        <div className={classes.appBarSpacer} />
        <Container maxWidth="lg" className={classes.container}>
        <Grid container spacing={3}>
        <Grid item xs={12}>
        <Box>
        <Typography variant="h1" style={{ border: "1px solid black" }}>
          Hello
        </Typography>
        </Box>
        </Grid>
        </Grid>
        </Container>
        </main>
        </div>
      );
    }
    

https://i.stack.imgur.com/DfSXj.png

give this a shot!

const customStyles = makeStyles((theme) => ({
root: {
    flexGrow: 1,
    [theme.breakpoints.down('sm')]: {
        marginBottom: 56,
    },
    [theme.breakpoints.up('sm')]: {
        marginBottom: 64,
    },
},
menuButton: {
    marginRight: theme.spacing(1),
},
title: {
    flexGrow: 1,
}, }))

You can incorporate the above snippet into your code in this manner

const NavigationBar = () => {
const classes = customStyles()
return (
    <div className={classes.root}>
        <AppBar position='fixed' color='primary'>
            <Toolbar>
                <IconButton
                    edge='start'
                    className={classes.menuButton}
                    color='inherit'
                    aria-label='menu'>
                    <MenuIcon />
                </IconButton>
                <Typography variant='h6' className={classes.title}>
                    News
                </Typography>
                <Button color='inherit'>Login</Button>
            </Toolbar>
        </AppBar>
    </div>
)}

To explore further insights, check out material-ui breakpoint customization

One quick trick is to use the position property set to sticky for the Appbar. Check out the image linked below for a visual reference!

click here to view the image

In developing my Vite-React application, I encountered a challenge with the MUI ResponsiveAppBar component. Despite attempting various methods to customize the bar's attributes as suggested, I found that the bar was unaware of other components on each page, leading to unsuccessful results. To overcome this issue, I implemented a solution by defining a CSS class within index.css:

.content-container {
margin-top: 80px;
}

Subsequently, I incorporated this class into each page's rendering div element for additional components. As an example, in the homepage:

import React from "react";

function HomePage() {
    return (
        <div className="content-container">
            <h1>Home Page of App</h1>
        </div>
    )
}

export default HomePage

By including this approach, a designated margin can be established at the top of the page to prevent overlapping with the appbar and surrounding content. Through testing, I confirmed that this adjustment does not compromise the app's responsive functionality.