A Bitcoin node is not software or a machine...
It is a person who actively decides what Bitcoin is by connecting to their preferred version when required.
During times of peace, no connection is necessary (for this specified purpose -there are other reasons, see links below).
During war, eg 2017, only those making a choice are nodes.
If a person connects their wallet to Parmanode or Star9, or Umbrel, but doesn't agree with it when push comes to shove, they are not a node.
So it's not just copies of the blockchain in active sync, because if it was just about that, it's plenty redundant.
Fundamentally it's people who are not passive.
The software is just to help them be an active participant when required.
Six reasons why you should run your own Bitcoin Node – Bitcoin Guides
Understanding Decentralisation in Bitcoin – Bitcoin Guides
