With the release of iOS 13, iOS NFC core framework has added API's to write on NFC tags. But does this mean that now we can transfer data between two iPhone devices using NFC APIs.
Writing and reading on NFC tags works fine.
Not directly between two phones. You can read from a tag and write to a tag, but iOS doesn't provide support for Card Emulation.
This means that you can't make iPhone "A" look like a tag, which is what would be necessary for iPhone "B to read data directly.
iPhone "A" could write some data to a tag, which iPhone "B" then read, but it would be quite cumbersome.