OnePlus
Does the OnePlus 9 Pro support eSIM?
No, the OnePlus 9 Pro has no eSIM and only works with a physical SIM.
The OnePlus 9 Pro does not have eSIM. For mobile data abroad you will need a physical (travel) SIM with this device, or roaming from your own provider.
Source: GSMArena
Check your OnePlus 9 Pro for an eSIM yourself
Dial *#06# on your phone. A 32-digit EID number means your phone has an eSIM. On iPhone check Settings > General > About; on Android check Settings > SIM manager.
Frequently asked questions about the OnePlus 9 Pro
Can I use an eSIM on the OnePlus 9 Pro?
No. The OnePlus 9 Pro is not eSIM-compatible and only works with a physical SIM. For mobile data abroad you'll need a physical travel SIM with this device.