Only start animation if window is undecorated and a target component is set.

core/src/main/java/com/github/weisj/darklaf/ui/tooltip/DarkToolTipUI.java

@@ -397,10 +397,16 @@ public class DarkToolTipUI extends BasicToolTipUI
             super(FADEIN_FRAMES_COUNT, FADEIN_FRAMES_COUNT * 15, false);
         }
 
+        @Override
+        public boolean isEnabled() {
+            return toolTip.getComponent() != null && super.isEnabled();
+        }
+
         @Override
         public void paintNow(final float fraction) {
             alpha = fraction * MAX_ALPHA;
             Window window = SwingUtilities.getWindowAncestor(toolTip);
+            if (DarkUIUtil.isDecorated(window)) return;
             if (window != null) window.setOpacity(alpha);
             Border border = toolTip.getBorder();
             if (border instanceof DarkTooltipBorder) {
@@ -412,7 +418,7 @@ public class DarkToolTipUI extends BasicToolTipUI
         protected void paintCycleEnd() {
             alpha = MAX_ALPHA;
             Window window = SwingUtilities.getWindowAncestor(toolTip);
-            if (window != null) {
+            if (window != null && !DarkUIUtil.isDecorated(window)) {
                 window.setOpacity(alpha);
                 Border border = toolTip.getBorder();
                 if (window.getFocusableWindowState() && border instanceof DarkTooltipBorder) {

core/src/main/java/com/github/weisj/darklaf/util/DarkUIUtil.java

@@ -528,4 +528,10 @@ public final class DarkUIUtil {
         if (type != null && type.isInstance(o)) return type.cast(o);
         return null;
     }
+
+    public static boolean isDecorated(final Window window) {
+        if (window instanceof Frame) return ((Frame) window).isUndecorated();
+        if (window instanceof Dialog) return ((Dialog) window).isUndecorated();
+        return false;
+    }
 }