Script for selecting the above layer with the current one

// add the next layer above to the selected;
// 2022, use it at your own risk;
if (app.documents.length > 0) {
    var ref = new ActionReference();
	ref.putEnumerated( charIDToTypeID("Dcmn"), charIDToTypeID("Ordn"), charIDToTypeID("Trgt") );
	var desc = executeActionGet(ref);
	if (desc.getBoolean(stringIDToTypeID("hasBackgroundLayer")) == true) {var theAdd = -1}
    else {var theAdd = 0};
// get the active layer’s index;
    theIndex = getLayerIndex() + theAdd;
    var theCheck = false;
    while (theCheck == false) {
        theIndex++;
        var ref = new ActionReference();
        ref.putIndex( charIDToTypeID( "Lyr " ), theIndex);
        var layerDesc = executeActionGet(ref);
        var layerSet = typeIDToStringID(layerDesc.getEnumerationValue(stringIDToTypeID("layerSection")));
        var theName = layerDesc.getString(stringIDToTypeID('name'));
// if not group end collect values;
        if (layerSet != "layerSectionEnd") {
            theCheck = true
        };
    };
    selectLayerByIndex(theIndex--,true)
};
////// by mike hale, via paul riggott //////
function getLayerIndex(){
    var ref = new ActionReference(); 
    ref.putEnumerated(charIDToTypeID("Lyr "), charIDToTypeID("Ordn"), charIDToTypeID("Trgt")); 
    d = executeActionGet(ref); 
    return d.getInteger(stringIDToTypeID('itemIndex')); 
    };
////// by mike hale, via paul riggott //////
function selectLayerByIndex(index,add){ 
    add = undefined ? add = false:add 
    var ref = new ActionReference();
        ref.putIndex(charIDToTypeID("Lyr "), index);
        var desc = new ActionDescriptor();
        desc.putReference(charIDToTypeID("null"), ref );
           if(add) desc.putEnumerated( stringIDToTypeID( "selectionModifier" ), stringIDToTypeID( "selectionModifierType" ), stringIDToTypeID( "addToSelection" ) ); 
          desc.putBoolean( charIDToTypeID( "MkVs" ), false ); 
       try{
        executeAction(charIDToTypeID("slct"), desc, DialogModes.NO );
    }catch(e){
    alert(e.message); 
    }
    };

@Johnnyenv as @c.pfaffenbichler mentions, using keyboard shortcuts work in most situations... Layer visibility and having an expanded layer group directly above the active layer may cause issues.

OPT + ] and then CMD + E

ALT + ] and then CTRL + E

or

OPT + SHIFT + ] and then CMD + E

ALT + SHIFT + ] and then CTRL + E

Would both lead to the same result and can also be recorded into an action or into ScriptListener code.

Why don’t you use the default keyboard shortcut? 

The index would seem to offer a fairly convenient way to determine the Layer above the currently selected one. 

How far have you gotten with the Script yet?