By "real" on-chain transaction I mean "actual" on-chain transaction, ie. a transaction recorded on the blockchain. When people buy or sell bitcoins on exchanges

By "real" on-chain transaction I mean "actual" on-chain transaction, ie. a transaction recorded on the blockchain. When people buy or sell bitcoins on exchanges, nothing is recorded on the blockchain. Instead, an exchange records a trade on their internal infrastructure (however it's implemented: a database, a log file, whatever). It's not done on the blockchain.