Wie viele Bitcoins gibt es im Umlauf?

Could you elaborate on the circulating supply of Bitcoins? I'm curious to understand the exact number of Bitcoins that are currently available and in circulation. Given the finite nature of Bitcoin's supply, it's important to grasp how many have already been mined and are actively being used in the market. Could you provide a brief overview of the current circulating supply, and perhaps mention any factors that might affect its future growth or decrease?