Whenever I have had my cat on a leash and we're heading home again in the backpack, he starts complaining and tries to get out (he's not scared or afraid, just frustrated the walk has ended).
It's really important that he learns to ride in the backpack, as we'll have to travel sometimes and he'll have to stay put. But I know he really enjoys being out on the leash, so of course I want to do that sometime too.
Even though he's complaining when I put him back in the backpack, it is also his safe space, so I can't let him out when walking back home (I have tried, and he freaked out by the sounds of a motorcycle and clawed his way up on my shoulders).
He's only 5 months, and there's still a lot to learn. And since riding in the backpack and being able to travel - meaning I'm focusing on desensitizing him to traffic, busses and trains. I also want to sometimes let him out on the leash somewhere in nature, that he enjoys, so he doesn't learn that going out is always a little stressful or boring. But I really need him to learn that when he's in the backpack, he has to stay put.