Amazon has higher retail sales than Walmart?

Yes, Amazon does more retail sales than Walmart. Their "revenue" is only 15% on all third party sales, which are now more than half of total sales on the platform. They don't report on total sales on the platform on purpose to avoid drawing attention to the fact that they are bigger than Walmart.

I think amazon may have higher total sales on its platform, but like 60% of their sales are actually sold by other marketplace sellers, not Amazon.

Walmart meanwhile does also have a marketplace, but I think still sells the overwhelming majority of their stuff direct in their physical stores.

Remember Walmart has revenue of like 600 billion a year or something crazy.

Shopify for comparison is almost half the size of Amazon Marketplace but on trajectory to match it in the next two years.

But that 15% that amazon takes (not counting the extra cut they take for Fulfilled by Amazon items) is larger than Walmart's average markup. So that isn't really an argument against their size.

That question mark is confusing

If you have to ask what it symbolizes - it doesn't

I'm not confused by it, though I'm a native English speaker and live in an English speaking country and spend most of my internet time on English speaking internet, so maybe that's why