Here's a Material-UI faded text effect based on Mahan Lamei's suggestion:
Create the overlay style
const useStyles = makeStyles((theme) =>
  createStyles({
    fadeText: {
      background: `linear-gradient( 180deg, #FFFFFF00, 0%, #FFFFFF06 30%, #FFFFFFFF 100%)`,
      pointerEvents: "none",
    }
  })
)
Next overlay a gradient on a fixed-height nested Box component
<Grid container justify="center">
  <Grid item xs={8} sm={6} md={4}>
    <Box>
      <Box
        component="div"
        overflow="hidden"
        display="flex"
        flexDirection="column"
        fontFamily="Roboto"
        fontSize="body1.fontSize"
        fontWeight="fontWeightLight"
        textAlign="justify"
        height={['8rem']}
      >
        <Box display="flex">
          Lorem ipsum dolor sit amet, consectetur adipiscing
          elit, sed do eiusmod tempor incididunt ut labore
          et dolore magna aliqua. Ut enim ad minim veniam,
          quis nostrud exercitation ullamco laboris nisi ut
          aliquip ex ea commodo consequat. Duis aute irure
          dolor in reprehenderit in voluptate velit esse
          cillum dolore eu fugiat nulla pariatur. Excepteur
          sint occaecat cupidatat non proident, sunt in
          culpa qui officia deserunt mollit anim id est
          laborum.
        </Box>
      </Box>
      <Box
        className={classes.fadeText}
        display="block"
        position="relative"
        top="-4rem"
        height="4rem"
      />
    </Box>
  </Grid>
</Grid>
Working demo: Codesandbox
MUI's default theme uses abbreviated CSS colors (#FFF) so if you want to set your gradients based on the current theme you will need to override them with the full six character variants.
Example: using theme to set the gradient (e.g. based on the light/dark theme):
const useStyles = makeStyles((theme: Theme) =>
  createStyles({
    fadeText: {
      background: `linear-gradient( 180deg, ${theme.palette.background.paper}00 0%, ${theme.palette.background.paper}06 30%, ${theme.palette.background.paper}FF 100%)`
    } 
  })
)
Edit: Updated to include Tony Bogdanov's suggestion