"Reserve Currency" is a term used a lot in conspiracy theory circles. IMO, it's mostly a waste of time to think about as something that will change in our lifetimes. Maybe our children's lifetimes.
The USD being a reserve currency just means most other countries hold their currency reserves in USD. Related, a lot of worldwide financial instruments are denominated in USD, even when the US is not part of the transaction. For example, oil contracts are USD denominated, even if the contract parties are Saudi Arabia and Japan.
There's no governing body out there that declares USD as the reserve currency. It's just what most countries choose to hold their reserves in because it is a stable and predictable currency. There aren't any other choices out there with the same dependability. Your conspiracy theory articles will usually point to the Yuan. Nevermind that the Yuan was pegged to the USD until 2015, and it still isn't a fully convertible currency. The euro also has some significant issues.
If something else were to take place of the USD, it would likely mean higher interest rates for the US and a weaker dollar. The US would import less and export more. Absent thermonuclear war, this is the type of change I would expect to happen over decades as countries slowly diversified their reserves. It wouldn't be an overnight event that you could trade.