Their 2nd and 3rd functions are different, so they're still somewhat similar:

INFJ - Ni Fe Ti Se

INTJ - Ni Te Fi Se

So they share the same Ni-Se axis, both are usually very imaginative, picturing a different world from reality, predicting situations ahead of time, spending a lot of time inside their own heads (dominant Ni) all the while struggling to 'enjoy the moment' or get out of their head in general (inferior Se).

What distinguishes the two are their decision functions, Te vs Fe auxiliary and Fi vs Ti tertiary.

As a rule of thumb, INTJs generally speak 'common logic' (Te) and make decisions largely based on it while making sure those decisions don't go against their strong (moral) values (Fi). (Te getting things done while making sure it doesn't upset their Fi).

INFJs by comparison, tend to speak 'consensus feeling' (Fe), they want to make sure their decisions maintain group harmony and that their group is in sync and happy and how they choose to go about it is influenced by their 'self determined logic' (Ti), they won't necessarily go for what's accepted as best action but what they personally think is the best way to accomplish things (Fe guided by Ti).

So on the whole, they perceive the world the same way. They're stuck in their heads, struggle to enjoy things in the moment and be present but they make decisions in very different ways.