Example using controlled Mui Select

// https://mui.com/material-ui/react-select/
import React, { useState, useEffect } from 'react'
import { FormControl, InputLabel, Select, MenuItem } from '@mui/material'

export default function App() {
    const [age, setAge] = useState('')

    const handleChange = (event) => {
        setAge(event.target.value)
    }

    useEffect(() => {
        // установить значение через секунду после загрузки страницы
        setTimeout(() => {
            setAge(10)
        }, 1000)
    }, [])

    return (
        <FormControl fullWidth>
            <InputLabel id="demo-simple-select-label">Age</InputLabel>
            <Select
                labelId="demo-simple-select-label"
                id="demo-simple-select"
                value={age}
                label="Age"
                onChange={handleChange}
            >
                <MenuItem value={10}>Ten</MenuItem>
                <MenuItem value={20}>Twenty</MenuItem>
                <MenuItem value={30}>Thirty</MenuItem>
            </Select>
        </FormControl>
    )
}