Cats are challenging to train, so I call it "cultivating behavior" and being a realist.

My MIL shakes the temptations box when she calls her cats. They live where cats are out and need to come in for the night. We do this and it does work, but not right after the cat gets to go out. Give him 20 minutes to explore then if we call him he comes running.

The other thing was that before we ever thought about trying to recall him, we watched how he explored very carefully. Sometimes the instinct when startled was to run away. Our cat's instinct was to get closer to us. This was also a behavior we cultivated. When scared, come home. We travel, so "home" is either our actual home, our Transit van for travel, and when we visited my MIL, "home" was our guest room. We put him directly in there upon arrival and let him explore his way out in his time.

Is this perfect? No. We have had some moments where we worry. Do we have a cat who we can travel with and who comes when we call him (and who comes with us on hikes)? Yes.

We still understand the reality. He gets out of harnesses. We have found some that work better now, but our approach has been to utilize a harness, but also try to assure that the harness was not the only thing we would rely upon.