How to fix closure "expects 1 argument, but 2 were used in closure body" when using enumerated().map

Question

I have the following Swift code which uses enumerated().map to index my modeStrings:

let modeNames = [
            "Rest: ",
            "Misbalanced: ",
            "Left Charged: ",
            "High Voltage: ",
            "High Temperature: ",
            "Low Temperature: ",
            "Low Voltage: ",
            "Hibernation: ",
            "Over Discharge Current: ",
            "Ship: "
        ]
        var modeStrings = [
            deviceData.restMode,
            deviceData.misbalancedMode,
            deviceData.leftChargedMode,
            deviceData.highVoltageMode,
            deviceData.highTempMode,
            deviceData.lowTempMode,
            deviceData.lowVoltageMode,
            deviceData.hibernationMode,
            deviceData.overDischargeMode,
            deviceData.shipMode
        ]
        
        let indexAndNum = modeStrings.enumerated().map { (index: Int, element: inout String?) in
            let value: String
            if Int(data[28 + index]) == 1 {
                value = "On"
            } else {
                value = "Off"
            }
            let formattedString = (modeNames[index] + value)
            element = formattedString
        }
    }

My problem is I get an error Contextual closure type '(EnumeratedSequence<[String?]>.Element) throws -> ()' (aka '((offset: Int, element: Optional<String>)) throws -> ()') expects 1 argument, but 2 were used in closure body

This error goes away if I remove the inout keyword but then I get this error: Cannot assign to value: 'element' is a 'let' constant.

element is referring to my modeStrings which is of the type [String?]. How can I assign a value to element without using inout? Or am I just using inout incorrectly?