Nibbāna is NOT like anything a run-of-the-mill person has ever known.
The reason is: Nibbāna is unconditioned dhamma while a run-of-the-mill person has only ever known or experienced conditioned dhamma for his/her entire lifetime so far. (At the moment such a person knows or experiences nibbāna, he/she is no longer called a run-of-the-mill person, he/she has become a noble discipline)
So, trying to describe nibbāna “to be like” or “similar to anything” to a run-of-the-mill person, it becomes an unprecise attempt and must be taken with much care for deviation.
Now back to your question about nibbāna and mind-objects, my answer to you is: mind-objects are conditioned while nibbāna is unconditioned.
I will try to give another example here but as I have just explained above, please do not cling to example.
Let’s see an example between a tadpole and a frog:
A frog can try but can not fully explain what it’s like an experience so called “out of water” to a tadpole. Meanwhile, a tadpole can try its best with fantasy, imagination, speculation, etc. but in the end, a tadpole who is deeply submerged in water won’t be able to fully know or experience the so called “out of water” land.
Any tadpole who is near the water level will have a chance to be able to have a glimpse of the land and know there is such a thing so called “out of water”. Such tadpole is no longer a normal run-of-the-mill tadpole, it has known and it has faith in what the frog said. But only until a tadpole completes its metamorphosis process to become a frog, it still does not experience yet the “out of water”. Note of humor: In the nature, a tadpole won’t need to follow the Noble Eightfold Path taught by a frog. So, you see here the limitation of an example.