Use another Macbook Pro with touchbar as secondary screen

You cannot use your MacBook Pro in Target Display Mode nor achieve the same result via a ThunderBolt 3 (USB-C) cable to connect it to the other MacBook Pro.

However, there are other options you can investigate, but I have no personal experience with them. Two of these options are listed below:

• Air Display
• Mirroring360

In summary, they promise to allow users to share their Mac screens on a variety of devices, including other Macs.

Another option which may be worth investigating, is using VNC to share the screen from one MBP to the other - but this may not give you what you want.

You can only use iMac as a secondary screen with Mini DisplayPort to Mini DisplayPort. Target Display Mode lets you use the built-in display on a supported iMac as an external display for another Mac. To use your iMac as a display in Target Display Mode, connect it to another Mac using the correct cable (see System Requirements below).

However,

Connecting two MBPros to create an extended screen won't work. Use VNC viewer as Remote Desktop if you want else I don't see any option as I am daily working on Apple devices and people has come up with this request many time.