Our bigger dog (maltese plus a few other odds and sods crossed) does exactly the same, but she uses the puppy door that the smaller dog fits through.
I now think there is a game of “In / Out” going on. The goal of the game is to see how often she can convince me to get up and let her out and then let her back in again.
If they both want to come in together, the little one puts her feet on the back door glass and starts scratching furiously on it until I get there. If it’s just her, she comes in her puppy door.
We have glass doors to the outside. Our old dog taps it with his paw to go out. Our younger dog goes to the door, then comes back to us, and then repeats until we get it.
The dog has access to the back yard whenever he needs it, but he still wants to be walked a couple of times a day. If I’ve been sitting in one place too long, he’ll ram his muzzle up under my elbow and maneuver his head so my leash hand is on his collar.
My poor girl: the snow is up over her head and she had no where to go. She peed on the end of the porch and then looked guilty. Once it stopped I went out and cleared a patch for her. She’s not happy because she likes to go somewhere where I can’t see her, but I wasn’t about to clear that much snow just for her to go.
Both of our dogs come over and go : " Murf murf murf" at us until we get up and go. If that fails then they will hop up for a hug to get out attention before resuming the murfing.
Auggie, The Cutest Dog on the Planet, will paw at the door. His aim sometimes isn’t all that great, so the grasscloth on the wall next to the door is pretty much gone. On the rare occasions that he has to go in the middle of the night, he comes to my side of the bed and barks.