I am looking at Core NFC to figure out if it is possible to make the device itself as nfc tag? I need to read data from iOS/Android devices with iOS tag reader. If not possible, any other recommendation you guys have? I have read beacon/nearby message as possibility. Thank you!
No, CoreNFC APIs on iOS only allow scanning tags, and on iOS 13+ also allow writing tags. CoreNFC APIs do not allow emulating tags for third party apps.
An alternative for short-range data transfer on iOS and Android is using Bluetooth LE beacons. For it to emit data, with Bluetooth LE, and iOS app must generally be in the foreground. Data transfer is limited to about 20 bytes using non-iBeacon formats, or 4 bytes with iBeacon. If you require that the beacon signal strength be very high, you can roughly approximate the required range of NFC for BLE beacon data transfer.