So this pops up quite frequently, sometimes with the Seven Years War, sometimes the Thirty Years War, sometimes the Napoleonic Wars or some other conflict. Usually after som youtuber or blogger posts something along the lines of "This was the REAL first world war". Controversy sells after all. So are they wrong?

Yes, basically. There is a difference between a world war and a global conflict. World War I and II are the only wars commonly refered to as World Wars but they are far from the first or only global conflicts. From about the Age of Sail and onwards most wars between major powers had at least some fighting, especially naval engagements, all over the globe. The Anglo-Spanish wars had fighting on several continents. So did the Dutch-Portugese war and then obviously the Wars of the Spanish Succession, the War of Austrian Succession, the Seven Years War, The American and French Revolutionary wars, the Napoleonic wars and the Crimean War. So why aren't these wars considered world wars?

Because we don't call them that. It's that simple. Wars are not named by shadowy cabals of historians convening in ivy covered marble halls at midnight (although they absolutely should be), they are named by a far less prestigeous process that goes something like this: News papers publish a variety of material on "the war" and usually people know which one they mean because hopefully your nation is only involved in one, they give them a variety of names at first until one just becomes popularly accepted by no structured process what so ever.

So, it comes down to this:

World War - Just a name we use for two particular wars in the 20th century. There are precisely two of these.

Global conflict/war - A war usually defined as having engagements over two or more continents or having participants from two or more contients. There are tons of these from the late bronze age collapse 1200 BC to, technically, the ongoing war in Syria.