To add MEWconnect Protocol to Web3Modal. Add MEWconnect to your Web3Modal provider options and supply your infura id.

Web3Modal Documentation

Install With NPM

npm install @myetherwallet/mewconnect-web-client

Add to Web3Modal

import { MewConnect } from '@myetherwallet/mewconnect-web-client'

const providerOptions = {
    mewconnect: {
      package: MewConnect,
          options: {
            infuraId: process.env.REACT_APP_INFURA_ID
          }
    },
};