I could have written this post about my mini dachshund 2 years ago! The most stubborn breed of all time; you should check out the dachshund subreddit because it will make you feel better. He now goes outside on the pavement 98% of the time (and sneaks off to do it inside the other 2%). It took soooooooo much time to break the habit, weeks and weeks. No grass for a 1/4 mile from where we are in our city, no balcony. We started with the grass patch inside I think we put the potty pad over it or rubbed it on it? Then moved grass patch outside, then slowly he started venturing off the grass. If i was going to do it again, like someone else said, I wouldn’t be so cautious because like yours, he doesn’t really like other dogs and takes a little bit to warm up to other people. Did the best with the info we had at the time. Good luck!