How is it possible, that nobody can track anyone on the bitcoin network? Is it possible that a person on the bitcoin network cannot be tracked?
I was studying, no one can track a person on the bitcoin network. Is that true?

Users can be tracked IF they don't follow the best practices. Although lot of on-chain analysis and investigation works on assumptions.
How?

Every transaction on-chain has lot of information associated with it including address, amount, type of transaction etc.
Not every user runs their own full node with tor
Some users share information related to transactions on social media

Best practices:

Use non-kyc non-custodial exchanges
Use full node with tor
Do not share information about transactions on social media
Use coinjoin, payjoin etc.
Do not reuse addresses