Does the OnePlus Open have eSIM? Yes

Yes, the OnePlus Open supports eSIM, so it can take a travel eSIM as long as it is carrier unlocked.

What to know about the OnePlus Open

OnePlus names the Open among its eSIM phones. Add one in Settings > SIM card & mobile data > Manage eSIM Card (OnePlus Support).

It takes an eSIM, so you can buy a data plan now and install it before you fly. Pick your destination.

Two minutes on the phone itself settles it, whichever version you have.

Dial *#06#
Open the phone app and dial *#06#. If a number labelled EID appears, your phone supports eSIM.
On Android
Go to Settings, then Network and internet, then SIMs. If you can add an eSIM or download a SIM, it supports eSIM.
Check it is unlocked
A phone bought from a carrier on contract may be locked to it. Ask your carrier, or look for a Carrier Lock line in your settings that says No SIM restrictions.

Set it up before you fly and keep your usual number for calls and texts.

The 30-second check for any phone: the EID, and whether it is unlocked.