npm install cypress-clipboard;

yarn add cypress-clipboard

import 'cypress-clipboard';

cy.get('SOME SELECTOR')
    .invoke('text')
    .copyToClipboard(); 

import 'cypress-clipboard';

cy.wrap('SOME STRING VALUE')
    .copyToClipboard(); 

import 'cypress-clipboard';
cy.copyFromClipboard().then(clipboardData => {})

import 'cypress-clipboard';
cy.copyFromClipboard().should('eq', 'EXPECTED VALUE');