How many Ethereum are in supply?

Could you please elaborate on the current supply of Ethereum? Understanding the current distribution and availability of this digital currency is crucial for investors and market analysts. I'm interested in knowing if there's a fixed or variable supply, and if there are any plans for future changes in the total supply. Additionally, it would be valuable to know if there are any mechanisms that regulate the supply, such as mining rewards or token burns. Could you provide an estimate of the current number of Ethereum in circulation and how it may evolve in the future? Thank you for your assistance in clarifying this important aspect of the Ethereum ecosystem.