JS Snippet to mass unwatch Repos when you are added into a team with 8486578561285 repos...

unwatch.js

(function() {
let qx = $x;
let unwatch = function(org, notificationType) {
  let nodes = document.querySelectorAll('.Box-row');
  let rows = [ ...nodes ];
  let orgRows = rows.filter(e => e.innerText.startsWith(`${org}/`));
  let orgUnsubButtons = orgRows.map(row => row.querySelector(`button.SelectMenu-item[value="${notificationType}"]`));
  orgUnsubButtons.forEach(button => button.click());
  setTimeout(function() {
  }, 1000);
};

let org = 'ORG'; // <--- change ORG to desired organization, and repeat for all pages. CASE sensitive
let notificationType = 'included'; // 'included' = participating and @mentions, 'subscribed' = all activity, 'ignore' = ignore
unwatch(org, notificationType);
})();