Step 1 - Set Opacity to 0% on Frame 2, 3, and beyond
On all layers and groups in Frame 2, Frame 3, and any additional frames, go to Edit and set the Opacity slider to 0%. This prevents those layers from interfering with your end frame.
Step 2 - Add an Opacity animation to those layers
For each layer or group you just set to 0% opacity, add a new Opacity animation. Set it to 0.1 on the timeline and choose "End with 0%" in the settings.
Step 3 - Update your other animations
For all other animations that fade elements in or out, update their settings to "End with 100%". Then enable the "Only on repeat" checkbox - this makes sure those animations do not run on the final loop of the ad.
Step 4 - Update Frame 1
On Frame 1, find the last animation that fades out your layer or group. Enable "Only on repeat" on that animation so your end frame stays fully visible on the final loop.