The Samsung Galaxy SmartTag is compatible with Galaxy devices (including phones and tablets) that can run Android 8 software or later.
However for the SmartTag Plus, you'll need a Galaxy device with UWB technology to be able to make use of the ultra-wideband features, and this tech is usually only found with the latest Samsung smartphones running Android 11 – such as the Samsung Galaxy S22 and the latest Samsung Galaxy S23 models.