@Composable
fun PulsePressure() {
    var systolicTextFieldValue by rememberSaveable(stateSaver = TextFieldValue.Saver) {
        mutableStateOf(TextFieldValue())
    }
    var isSystolicTextFieldValueError by rememberSaveable { mutableStateOf(false) }
    var diastolicTextFieldValue by rememberSaveable(stateSaver = TextFieldValue.Saver) {
        mutableStateOf(TextFieldValue())
    }
    var isDiastolicTextFieldValueError by rememberSaveable { mutableStateOf(false) }
    InputWithUnitContainer(
        systolicTextFieldValue,
        isError = {
            isSystolicTextFieldValueError = it
        },
        incrementTextFieldValue = {
            systolicTextFieldValue = it
        })
    InputWithUnitContainer(
        diastolicTextFieldValue,
        isError = {
            isDiastolicTextFieldValueError = it
        },
        incrementTextFieldValue = {
            diastolicTextFieldValue = it
        }
    )
}

@Composable
fun InputWithUnitContainer(
    textFieldValue: TextFieldValue,
    isError: (Boolean) -> Unit,
    incrementTextFieldValue: (TextFieldValue) -> Unit,
) {
    val maxLength = 4
    Row(
        modifier = Modifier
            .fillMaxWidth(),
        verticalAlignment = Alignment.CenterVertically
    ) {
        TextField(
            value = textFieldValue,
            singleLine = true,
            onValueChange = {
                if (it.text.length <= maxLength) {
                    incrementTextFieldValue(it)
                }
                isError(false)
            },
            isError = isError,
            textStyle = RegularSlate20
        )
    }
}

None of the following functions can be called with the arguments supplied.

InputWithUnitContainer(
    textFieldValue = diastolicTextFieldValue,
    isError = isDiastolicTextFieldValueError,
    updateIsError = updateIsDiastolicTextFieldValueError,
    incrementTextFieldValue = {
        diastolicTextFieldValue = it
    }
)

@Composable
fun InputWithUnitContainer(
    textFieldValue: TextFieldValue,
    isError: Boolean,
    updateIsError: (Boolean) -> Unit,
    incrementTextFieldValue: (TextFieldValue) -> Unit,
) {
    ...
}

TextField(
    value = textFieldValue,
    singleLine = true,
    onValueChange = {
        if (it.text.length <= maxLength) {
            incrementTextFieldValue(it)
        }
        updateIsError(false)
    },
    isError = isError,
    textStyle = TextStyle(),
)

So that's the right way to hoist state. But you might want to consider deriving the error state from the actual text

right now you've got two sources of truth for the error state, which is going to be harder to maintain and could introduce bugs.