No. T-Mobile usually says that everything must be initially activated on a T-Mobile US Network. However that doesn't mean you can't try and see if it works.

Hi! Thanks for reading this. 

I’ll be traveling long-term for a few months and I want to get a new plan for my work phone. The thing is, I’m already abroad. In Spain, to be exact. 

Will I be able to activate a brand new US phone number with the essentials eSim from abroad? The site kind of suggests otherwise but I’ve read others have been able to do so in the past. I’m curious about your experiences/advice. 

Thank you!

Can I activate the Essentials eSim plan abroad?