Here is my simple explaination about the <Theme, StyleProps>
makeStyles method from MaterialUI is using generic type for defining what u can use from their Theme variables and, props type that u want to assign.
 
Theme type imported from : import { Theme } from "@material-ui/core";
 
makeStyles() returning theme value that u can use, the 'Theme' is the type definition for that theme value.
 
Code Example :
#1 makeStyles using only the theme value :
const useStyles = makeStyles<Theme>((theme) => ({
  button: {
    background: theme.palette.background.paper,
    color: theme.palette.success.light
  }
}));
#2 makeStyles using theme value & your props :
const useStyles = makeStyles<Theme, StyleProps>((theme) => ({
  button: {
    background: theme.palette.background.paper,
    color: theme.palette.success.light,
    width: ({ md }) => "50%"
  }
}));
#3 makeStyles using only your props :
const useStyles = makeStyles<any /* <-- it doesn't matter what type u define here, because u doesn't use theme value*/, StyleProps>({
     button: {
       width: ({ md }) => "50%",
       background: "grey"
     }
    });
Hope this answer can help. :)