I've noticed myself doing this and I can pause it if I try but I don't think I can turn it off. Playing games as a kid, it was all about exploration and doing fun things. I didn't beat many games but I played a lot of them. As an adult, I need to be setting goals and earning achievements. There always needs to be something I'm working towards.
It's fun planning/achieving at first but after a few weeks it just feels like i've given myself another job then i get burnt out and reset.
I haven't played battlefield 2042. I bet you're right that portal mode is fun but I'm willing to bet if I was to play I would probably start to express the same sentiment that there's no point in playing portal mode if it doesn't help me progress in the game. It's stupid and I have a hard time admitting it but it's true.
Sometimes I wish I could just enjoy a game for what it is and not be thinking about "what next?" or "what does this accomplish?". I think its just because we're adults (and probably because we have fully developed prefrontal cortexes?)