Having the option and being able to complete the process of adding a 2nd esim are not the same. I guess you could buy/try it and see, you should be able to see locked status for both sims in either the ABOUT page or the CELLULAR page. That’s where mine was showing before the unlocked the phone and both sims.

You can always try and call them, maybe 611, not sure. There isn’t a page or portal for “my phone is locked and I still owe money on it, but want to travel int’l and not use ATT but a third party eSIM, will you unlock it”. Hard to tell. I’ve tried that before and they wouldn’t budge. YMMV, I thought having been an ATT mobility or mobile customer for ~ 33 years at the time would have helped, but it didn’t. I just ended up taking my prior years phone for the int’l sim.