Getting the name of plugin in selected insert slot

Chris mate!

This will get you the current insert Title ie. a-j ;

const insertPositionSelectorMenuTitle = sf.ui.proTools.windows.whoseTitle.is('Plug-in: EQ3 1-Band').first.popupButtons.whoseTitle.is('Insert Position selector').first.value.invalidate().value;

log(insertPositionSelectorMenuTitle);

This will get you the insert position selector menu items as an array;

const insertPositionSelectorMenuItemsArray =sf.ui.proTools.windows.first.popupButtons.whoseTitle.is('Insert Position selector').first.popupMenuFetchAllItems().menuItems.join(',').split(',');

log(insertPositionSelectorMenuItemsArray);

I'll work on comparing the title and the array items later.

That gets you half way there at least (if only they were checked items).

Rock on!

Here is the completed script. Thanks so much for your help (truly).
It cycles/steps through all the active inserts on a track while skipping inactive plugins or unassigned inserts.
I modified your script slightly to pass the active insert name and a flat insert array into the plugin object. I didn't need the button on it's own.

sf.ui.proTools.appActivate();
const sup = sf.ui.proTools
sup.invalidate();
sup.appActivateMainWindow();
try {
sup.floatingWindows.whoseTitle.contains('Plug-in:').first.elementRaise();
    function insertPositionPluginName() {
        //Insert Position selector button 
        const btn = sf.ui.proTools.windows.first.popupButtons.whoseTitle.is('Insert Position selector').first;

        //Button title ie 'a-j'
        let buttonTitle = btn.value.invalidate().value;

        //Menu Item String converted to Array
        let insertPositionSelectorMenuItems = btn.popupMenuFetchAllItems().menuItems.join(',').split(',');

        //Filter Menu Item array to select matched item
        let pluginNameFromArray = insertPositionSelectorMenuItems.filter(element => element.charAt(7) === buttonTitle);

        //Hack to close popup menu
        sf.ui.proTools.appActivateMainWindow();

        return {
            name: pluginNameFromArray,
            flatPluginlistMenuList: insertPositionSelectorMenuItems,
        }
    }

//Get active plugin name and Insert selector list
    let plugin = insertPositionPluginName();
    const activePluginName = plugin.name.toString();
    const flatPluginlistMenuList = plugin.flatPluginlistMenuList;
    
// Sort Flat plugin Menu List to show only inserts with plugins

    let sortedPlugins = flatPluginlistMenuList.filter(function (item) {
        let checkSlot = item.indexOf("(");
        return checkSlot == 9
    });
    sup.appActivateMainWindow();

    // determine index of current plugin
    let activePlugsIndex = sortedPlugins.length;
    for (var i = 0; i != activePlugsIndex; i++) {
        if (sortedPlugins[i].indexOf(activePluginName) != -1) { break; }
    }
    // open next plugin
    let nextPlugIndex = i + 1;
    if (nextPlugIndex == activePlugsIndex) { nextPlugIndex = 0; }
    sup.windows.whoseTitle.contains('Plug-in:').first.popupButtons.whoseTitle.is('Insert Position selector').first.popupMenuSelect({
        menuPath: [sortedPlugins[nextPlugIndex]],
    });
    // routine for no open plugin wincow or inactive window 

    if ((sup.focusedWindow.title.value) == "") {
        while ((sup.focusedWindow.title.value) == "") {
            nextPlugIndex = nextPlugIndex + 1;
            if (nextPlugIndex == activePlugsIndex) { nextPlugIndex = 0; }
            sup.windows.whoseTitle.is('').first.popupButtons.whoseTitle.is('Insert Position selector').first.popupMenuSelect({
                menuPath: [sortedPlugins[nextPlugIndex]],
            });

        }
    }

} catch (err) {
    log("Please open / select an active plugin window…", "");
    throw 0
}