"der/die/das" vs "am" superlative in front of a noun

Question

I found a couple of articles on the Internet about this question but it's still not completely clear to me.

The rule they give here is the following:

Use a form of "der/die/das" with the superlative if it is right in front of a noun. Otherwise, use "am" with the superlative.
Berlin ist die größte Stadt in Deutschland.
Berlin gefällt mir am besten.

But what about this sentence I found in the Collins Dictionary?

Wer hat am meisten Geld? ⇒ who has (the) most money?

The superlative here is right in front of the noun but we can still use am- form. Can someone explain please when this is possible?

I'm also wondering if there's any difference in meaning or usage between:

Wer hat das meiste Geld? vs. Wer hat am meisten Geld?

Answer 1

die größte Stadt Deutschlands

is an adjective modifying Stadt and telling us it's the largest one. Die [superlative] is an adjectival form which modifies a noun.

Das gefällt mir am besten

is an adverb telling how that pleases you. Am [superlative] is an adverb describing a verb, adjective or even another adverb

Wer hat am meisten Geld?

am meisten isn't modifying Geld; it's not an adjective but rather it's an adverb describing who has the most money

For your question about Wer hat das meiste Geld? vs. Wer hat am meisten Geld?: They have the same meaning and are interchangeable. I'll have to leave that to someone else (I'm not a native speaker,and Google Search, Google Trends, and Google nGram are giving conflicting results (Google Search and nGram are saying the former is more popular, while Trends is saying the latter is), plus I personally can't tell a difference but the latter sounds stranger to me.)

Answer 2

The issue originates in the nature of nouns you're using. Geld describes an unspecified amount of money, while Stadt clearly describes one city. You won't use am meisten with Stadt, as it has a defined quantity, but you can use it with Geld.

The semantic difference is very slight. I'd use das meiste Geld to emphasize that the amounts of money that are compared do not add up to a meaningful entity. As this superlative modifies the noun (like thekeyofgb pointed out), it forbids the existence of any larger amount of money. am meisten Geld does not modify the noun, so it is a more relative comparison which may be bound to a domain and may allow a higher-ranking entity which is not part of the comparison.

So, the extended rule is: You can use superlatives with am in front of nouns if they describe an unspecified quantity. Of course, this only works with the superlatives of viel and wenig, because they annotate quantity.