A carrier lock is a limit the original carrier puts on a contract phone. A locked phone accepts that carrier's SIM and cannot install our eSIM or another carrier's physical card. It is separate from whether the phone has eSIM hardware. The hardware check is in compatibility. This article is only about the lock.
On iPhone, read the status
Open Settings → General → About and find Carrier Lock. "No SIM restrictions" means unlocked. A carrier's name means the phone is locked to that carrier.
Android has no single menu
Brands do not share one screen for this. If the phone was bought at a subsidy during a contract, ask that carrier whether it is unlocked. A phone bought at full price from a retailer is usually unlocked, and "usually" is not a substitute for checking with whoever sold it.
Install only after you have confirmed the phone is unlocked. The steps are in the installation guide. If you already paid, the phone is locked, and no profile has been issued, send the order number through contact. A profile that was already issued is not taken back.