discourse/app/assets/stylesheets/common/select-kit/topic-notifications-button.scss

.topic-notifications-button {
  &.is-loading {
    @include unselectable;
    pointer-events: none;

    .d-icon-spinner {
      margin: 0;
    }

    .selected-name .d-icon {
      display: none;
    }

    .topic-notifications-options {
      opacity: 0.5;
    }
  }
}

// This is a weird fix for a weird issue in iOS/iPadOS, the browser freezes
// when changing the notification level while in the fullscreen topic footer.
// This prevents the selected option icon from being hidden while saving,
// and somehow that makes Safari happy.
.timeline-fullscreen {
  .topic-notifications-button.is-loading {
    .selected-name .d-icon {
      display: inline-flex;
    }
  }
}