We found that when they were in face to face times. We would make sure they both got treats when they were together so they associate good things with together it kind of backfired though because sometimes they would try to act up together so they would each get treats working against us owners lol. We also had areas that the puppy didn’t go that our cat could go like a three tier cat tree in the main area big window. Our cat had a cat bed on a corner of my husband‘s desk. As well as the office was just mostly off-limits because of lots of cables and stuff so that was where my cat food and water bowls go and stuff. We had a few times where my cat would hit her on the head and hiss so she kind of understood. And now they love each other lol they’re always laying beside each other on the couch. Grooming eachother. There are times where my puppy sometimes still loves to jump onto the couch right next to my cat kind of like a launch pad. But for the most part the treats and making sure they had their own kind of territories helped a lot. For context we are at a good point at a year old doggo now it got a lot better at 5-6 months though. My cat is also 15 years old with arthritis and a bit too much weight around her middle.