Worked somewhere, not anymore, but still subscribed to all the public repos? Here's a solution

unwatch_repos.ps1

$org = "YOUR_ORG_HERE"

# List org repos that you are subscribed to
$repos = gh api 'user/subscriptions?per_page=100' --paginate `
  --jq ".[] | select(.owner.login==`"$org`") | .full_name"

if (-not $repos) { Write-Host "You’re not watching any $org repos."; exit }

# Unsubscribe
$repos | ForEach-Object {
  $r = $_.Trim()
  if ($r) {
    Write-Host "Unwatching $r"
    gh api -X DELETE "repos/$r/subscription" | Out-Null
  }
}

# Verify: should print nothing
gh api 'user/subscriptions?per_page=100' --paginate `
  --jq ".[] | select(.owner.login==`"$org`") | .full_name"