How can connect an Yongnuo YN 600 EX RT flash as master with an Yongnuo YN 560 IV as receiver mode

Since the YN600EX-RT uses the Canon RT wireless radio protocol and the YN560 IV uses the older Yongnuo YN560/RF605/RF603 protocol, the YN600EX-RT can not communicate directly with the YN560 IV. They use the same wireless frequencies, but each uses a different "language" to communicate the same information.

The easiest solution would probably be to use a YNE3-RX receiver attached to the hot foot of the YN560 IV. That might allow you to set manual power remotely, but it might not. If the YNE3-RX doesn't fire the flash when directly attached to the YN560 IV hot foot, then you could either:

• Use a PC cord between the YNE3-RX and the YN560 IV to send a "fire" command. All adjustments to the flash settings would need to be made directly on the flash.
• Tape over the TTL contacts on the YNE3-RX and attach it to the hot foot of the YN560 IV. The receiver would only send a "fire" command to the flash via the main pin. All adjustments to the flash settings would need to be made directly on the flash.

You can't do it with radio protocols. And the YN-560 models don't do Canon's "smart" optical. So the only way to use the YN-600EX-RT as a wireless master to a YN-560IV as a slave without adding any addition gear (cable, YN-E3-RX, Phottix Laso Rx, etc.), is using the S1/S2 "dumb" optical slave modes on the YN-560 IV, and firing the YN-600EX-RT on-camera out of wireless master mode.

This is why a lot of us prefer Godox gear to Yongnuo gear: Yongnuo uses three, separate, mostly-incompatible radio systems (60x/560, 622, and RT), while Godox only uses one integrated system. What you cannot do with the YN-600EX-RT and YN-560IV is exactly what you can do with a Godox TT685 and TT600 (with remote power control and HSS).