Is combination LoRaWAN 1.0.x and enable external Join Server correct?

TTN V2 to V3 Upgrade
1

In the TTS CE console I register a device.
I select LoRaWAN version 1.0.2 and I can select external Join Server is enabled.

Why can I enable external Join Server?
Should this option not be available at ALL when selecting LoRaWAN version 1.0.x