Using #disabled on the submit button is the wrong solution because it communicates to the Drupal form API that the button is not expecting input. In other words, it causes Drupal to act as if the button were not there at all. Hence, clicking the submit button has no effect. This all makes sense from a security perspective, because normally you wouldn't want ...
You can do this by using $form_state->setResponse() together with TrustedRedirectResponse.
Create the dropdown, like this:
$form['select'] = [
'#type' = 'select',
'#title' => t('Select'),
'#options' = [
'https://google.com' => t('Google'),
// More links...
To open the link in a new tab, you can add this to your form: