How does one determine they have aphantasia? How do you know that you are not doing exactly this thing people call visualizing when you perform spatial reasoning?

No idea, but when people say they can visualize an apple and then say it feels like number 1 on that chart, I would say that my experience of whatever I'm doing when I'm 'visualizing' an apple is more like 4 or 5

https://twistedsifter.com/wp-content/uploads/2023/10/AppleVi...

I can only assume people are trying to accurately describe their own experience so when my experience seems to differ a lot it seems to me that there is more going on than just confusion about wording.