Usually the esims you're referring to are data only (have no number). The sim registration requirements throughout the world are only about sims that have numbers attached.
eSIMs are not data only, that is dependant on your plan. It is basically just a technology that allows the physical SIM card to run inside a VM on your phone.
All SIMs, even data only ones, have numbers. You might not know what it is, but it has one.
All SIMs, even data only ones, have numbers. You might not know what it is, but it has one.