I think that just means you haven't looked into the topic enough yet. I'm INTP and my partner is INTJ, and these two types are quite different in some ways. In fact, all the main functions are directed in opposites. However, they still share many personality traits, so a lot of the online tests can results in random outcomes for some people.
Im a bit weird. Sometimes i timeblock my entire week and other weeks i prefer no plan at all. I’m not convinced its a static, immutable thing
It's all about preferences. INTPs can become very extroverted with the right crowd for example. And people obviously change behaviors depending on mood, health, etc.. I also try to timeblock things sometimes, but it never lasts long. If you can withstand "no plan at all" for any periods longer than 1 day, you're most likely not an INTJ. 😅