I bounce between INTJ and INTP. This week, it's a P
Helps to focus on the functions, because Introverts are already split between P and J. (I'll spare you the explanation unless you want it).
Do you prefer the details, the nitty gritty of how something works?
Or do you prefer what you can do with it?
Pretend it's computers for a moment...
INTPs are all about building that perfect hardware system. Every spec should be just so, according to their individual Ti overthinking.
After it's built, they tend to just play games on it. Work is what they tell other people it's for.
An INTJ might care about having a good system, but for it's practical application. So they might build their own, say if they're a coder... but they chose the parts a bit more simply. Is that sufficient? Well reviewed? Ok done. There's not the perfectionist agonizing that Ti causes.
Then they get to work (probably coding or some necessary program) and they only play games to vent their feelings about other people or to socialize. Definitely not all day.
*A little bit of overgeneralizing, but here's hoping it might help.
** If you really can't feel like one type, it means you're definitely a high user of Ne, because that function feels like everything is possible as a rule, and hates confinement.