I'm working on Win 10 OS. And am going to install magento2-2.3 on my local computer. Which xampp version and composer version should I use?
The short answer: Don't!
The long answer: I tried to get magento running with Windows 10 and ran into several problems - most of them related to file-permissions, because Windows handles them very different than Linux does.
But to your problem: you are using composer version 2.0 and magento still needs version 1. You can do a
composer self-update --1
Choose the one with the recommended PHP version and Database from Magento docs.