Can I use Titan XP on MacBook? Is the Nvidia's Titan XP compatible with Apple's MacBook (mid-2017)? I have never used external GPU but it seems to be that you can use it on MacBook Pro.

However, MacBook doesn't have Thunderbolt.

Is it possible to use Titan XP on MacBook, with a connector like Thunderbolt to USB 3.1? Is the performance drained via the connector and not a good solution in general?

The use cases are deep neural net and I don't use gaming, for your information.
No you really need a Thunderbolt connection.

It wasn't until Thunderbolt 3 that the bandwidth of the protocol fully caught up with the idea. Realizing this, the group responsible for the spec created implementations with the possibility of some configurations being able to pass the video signal back to the computer it was boosting.

Using a External GPU with older Thunderbolt connections will not fully utilise the performance increase of an External GPU.