I am trying to fork Ethereum Main Net via Ganache. In order to do this, I need The URL of the existing chain's RPC server. Nevertheless, I can't find such URL anywhere. Can anybody suggest such URL?
If you want to fork the mainnet you obviously need some place to fork it from. So you need access to a node which uses the mainnet and you can then connect to it with RPC.
You can either run your own node and wait for it to synchronize, or use a public (free) node service such as Infura or Alchemy.