(Cypress v10) : You can have multiple config files. For example as well as

cypress.config.ts

I have

/cypress/configs/cypress.mobile.config.ts

and my mobile config uses

defu

node package to safely override specified values:

import { defineConfig } from 'cypress';
import defu from 'defu';

import defaultConfig from '../../cypress.config';

export default defineConfig(
  defu(
    {
      viewportWidth: 375,
      viewportHeight: 812,
      userAgent: 'Mozilla/5.0 (iPhone; CPU iPhone OS 13_2_3 like Mac OS X) Mobile/15E148',
      env: {
        device: 'mobile',
      },
      e2e: {
        excludeSpecPattern: ['**/e2e/site-monitoring/*', '**/e2e/keyboard-navigation/*'],
      },
    },
    defaultConfig
  )
);

You'd just need to readjust for test environment specific values. And run command is like:

cypress run --browser chrome --config-file cypress/configs/cypress.mobile.config.ts

https://docs.cypress.io/guides/guides/command-line#cypress-run-config-file-lt-configuration-file-gt