It's kinda weird when people will say a piece of media takes place in "Medieval times" and yet it's a fantasy world.

Sure, but those developments are very focused on manufacturing. Like off the top of my head, Skyrim represents it's farmers as either independent farmers who own their own land, or wage workers employed by those farmers. They travel to towns and bring their produce to the local markets, and seemingly own all of their produce. So what do the Jarls own? They're supposed to be lords, but they are really just generic governors. Similarly, it seems that anyone in Skyrim can cut down trees if they want to, they don't need logging rights to cut and sell wood.

The Witcher 3 has a much more fleshed out economy from what I've played (only about 15 hours). The farmers, from what I can tell, are mostly wage workers, but the world is very clearly an early modern setting minus gunpowder, rather than a middle ages setting.

Agriculture is a very good benchmark for examining how an economy is represented. When a medieval fantasy setting has serfs rather than proles on a farm, it's evidence that at the very least, the writer understands that different economic systems exist.

Middle Earth seems to work in its own way, which I'm happy about. The hobbits seem to be a fairly communal society, with noble families being mostly a formality. But crucially, hobbits seem to have their own understanding of productivity and economics, and thats fun and imaginative for a fantasy setting. The worst is when writers just crowbar capitalism into a feudal-inspired society because they can't imagine anything else.

While that was once true, you're off by like 500-1000 years on the timeline for gold being a commonly struck currency, depending on what part of the world we're talking about.

Early Lydian coinage was like 40-60% gold and the rest silver, in an alloy called Electrum.

The first gold and silver coinage was issued by Croesus in the 6th century BCE, and then Cyrus the Great ran with that bimetallic system when he introduced coinage to the Achaemenid Empire, but that was pretty much the only time til the 15th century Golden age of Genovese banking, almost two thousand years later that gold coinage was again commonly used.

The Roman accounting system was based around the as, which was a bronze or copper coin, and then multiples of that, which were generally issued in silver or alloys like orichalcum (brass).

Charlemagne introduced the Carolingian coinage system which was silver denominated. This was the official coinage for the HRE for a few hundred years and directly led to more recent coinage.

However, debasement of currency was quite common during both of these eras and while sterling silver was pretty much always used in the British for example, other supposedly equivalent coins struck elsewhere would have entirely different metal compositions and the values became really hard to track as a result, so the origins of coinage became a more important factor than the supposed face value.

Under the Milanese House of Sforza, Genoa basically had the first two banks in Europe and went absolutely buckwild financing the entire continent with gold coins backed by slavery and set the stage for the colonization of the new world and transatlantic slave trade over the next few centuries.

TLDR: In the middle ages, gold coins were something that most people would never see or touch, there's like a 2000 year gap surrounding this era in which the entire continent of Europe pretty much just didn't use gold coins for major denominations that people would actually use because they didn't have access to gold.

There's also a lot more nuance to how coinage was actually used (or how it wasn't) in the medieval economy, but I'm sure someone else will help elucidate this as this is something I don't know much about.