Do I have to download the whole blockchain to start a full node in Ethereum?
Sadly, yes, the Ethereum client must download all blocks and validate all transactions before the full node will be usable. This is somewhere around 2TB of data now for a full node, it can take a while.
There is also a difference between full nodes and archive nodes -- see https://ethereum.org/en/developers/docs/nodes-and-clients/#node-types
A full node has the entire state but not all blocks, and is currently ~600-700 GB according to https://etherscan.io/chartsync/chaindefault
Thank you for your answers