@sim_1 When we install Drupal "10.0.x", the "stable9" theme exists on the "co...

@sim_1 When we install Drupal "10.0.x", the "stable9" theme exists on the "core/themes" path. So there is no need to add an additional contributed project theme "stable".

The contributed project theme "stable" will effectively work the same but it's now dependent on something outside of Drupal core.

I have checked with the Option 2 approach and the site is working fine with that. I have not found any issues from the UI side.