How to iterate over a JsonVariant?

There is no iterator on JsonVariant because it would be ambiguous.

Before iterating on a variant, the program must cast it to either a JsonArray or JsonObject.

For instance, for an object:

for( const auto& kv : variant.as<JsonObject>() ) {
    Serial.println(kv.key);
    Serial.println(kv.value.as<char*>());
}

and for an array:

for( const auto& value : variant.as<JsonArray>() ) {
    Serial.println(value.as<char*>());
}

See: