Blend file list based on: https://blender.stackexchange.com/q/30444/ #Blender

blender-blend-file-uilist.py

import bpy
from bpy.props import IntProperty, CollectionProperty, StringProperty, EnumProperty
from bpy.types import Panel, UIList, PropertyGroup, Operator
from bpy_extras.io_utils import ImportHelper
import os
  

class CUSTOM_OT_actionsUIList(Operator):
    bl_idname = "custom.list_action"
    bl_label = "List Action"

    action: EnumProperty(
        items=(
            ('UP', "Up", ""),
            ('DOWN', "Down", ""),
            ('REMOVE', "Remove", ""),
            ('ADD', "Add", ""),
        )
    )

    def invoke(self, context, event):

        scn = context.scene
        idx = scn.custom_index

        try:
            item = scn.custom[idx]
        except IndexError:
            pass

        else:
            if self.action == 'DOWN' and idx < len(scn.custom) - 1:
                item_next = scn.custom[idx+1].name
                scn.custom_index += 1
                info = 'Item %d selected' % (scn.custom_index + 1)
                self.report({'INFO'}, info)

            elif self.action == 'UP' and idx >= 1:
                item_prev = scn.custom[idx-1].name
                scn.custom_index -= 1
                info = 'Item %d selected' % (scn.custom_index + 1)
                self.report({'INFO'}, info)

            elif self.action == 'REMOVE':
                info = 'Item %s removed from list' % (scn.custom[scn.custom_index].name)
                scn.custom_index -= 1
                self.report({'INFO'}, info)
                scn.custom.remove(idx)

        if self.action == 'ADD':
            bpy.ops.custom.blend_select('INVOKE_DEFAULT')            
            scn.custom_index = (len(scn.custom)) # (len(scn.custom)-1)

        return {"FINISHED"}


class CUSTOM_OT_blendSelect(bpy.types.Operator, ImportHelper):
    """This appears in the tooltip of the operator and in the generated docs"""
    bl_idname = "custom.blend_select"
    bl_label = "Blend Selector"
    bl_options = {'PRESET', 'UNDO'}

    # ImportHelper mixin class uses this
    filename_ext = ".blend"

    filter_glob: StringProperty(
            default="*.blend",
            options={'HIDDEN'},
            )

    # Selected files
    files: CollectionProperty(type=PropertyGroup)

    def execute(self, context):
        scn = context.scene
        
        # get the folder
        folder = (os.path.dirname(self.filepath))

        # iterate through the selected files
        for i in self.files:
            # generate full path to file
            path_to_file = (os.path.join(folder, i.name))   
            item = scn.custom.add()
            item.id = len(scn.custom)
            item.name = i.name # assign name of selected object
            item.path = path_to_file
        
        self.report({'INFO'}, "Files Added")
        return {'FINISHED'}


class CUSTOM_UL_items(UIList):

    def draw_item(self, context, layout, data, item, icon, active_data, active_propname, index):
        split = layout.split(factor=0.7)
        split.prop(item, "name", text="", emboss=False, translate=False, icon='FILE_BLEND')
        split.label(text="Index: %d" % (index))

    def invoke(self, context, event):
        pass   


class CUSTOM_PT_blendFiles(Panel):
    """Creates a Panel in the Object properties window"""
    bl_idname = 'OBJECT_PT_my_panel'
    bl_space_type = "TEXT_EDITOR"
    bl_region_type = "UI"
    bl_label = "Custom Blend File List"
    
    def draw(self, context):
        layout = self.layout
        scn = bpy.context.scene
        
        try:
            current_item = (scn.custom[scn.custom_index].name)
        except IndexError:
            current_item = ""
        
        rows = 2
        row = layout.row()
        row.template_list("CUSTOM_UL_items", "", scn, "custom", scn, "custom_index", rows=rows)

        col = row.column(align=True)
        col.operator(CUSTOM_OT_actionsUIList.bl_idname, icon='TRIA_UP', text="").action = 'UP'
        col.operator(CUSTOM_OT_actionsUIList.bl_idname, icon='TRIA_DOWN', text="").action = 'DOWN'
                
        row = layout.row()
        col = layout.column(align=True)
        rowsub = col.row(align=True)
        rowsub.operator(CUSTOM_OT_actionsUIList.bl_idname, icon='ZOOM_IN', text="Add Files to List").action = 'ADD'
        rowsub.operator(CUSTOM_OT_actionsUIList.bl_idname, icon='ZOOM_OUT', text="Remove File").action = 'REMOVE'
        
        
        row = layout.row()
        col = row.column(align=True)
        col.operator("custom.active_item", icon="CONSOLE")
        col.operator("custom.print_list", icon="WORDWRAP_ON")
        col.operator("custom.clear_list", icon="X")
        
        row = layout.row(align=True)
        row.label(text="Active Item is: {}".format(current_item))


class CUSTOM_OT_clearListItems(bpy.types.Operator):
    bl_idname = "custom.clear_list"
    bl_label = "Clear List"
    bl_description = "Clear all items in the list"

    def execute(self, context):
        scn = context.scene
        lst = scn.custom
        current_index = scn.custom_index

        if len(lst) > 0:
             # reverse range to remove last item first
            for i in range(len(lst)-1,-1,-1):
                scn.custom.remove(i)
            self.report({'INFO'}, "All items removed")

        else:
            self.report({'INFO'}, "Nothing to remove")   

        return{'FINISHED'}

# print button
class CUSTOM_OT_printListItems(Operator):
    bl_idname = "custom.print_list"
    bl_label = "Print Name, ID and Path to Console"
    bl_description = "Print all items to the Console"

    def execute(self, context):
        scn = context.scene
        for i in scn.custom:
            print ("Blend-File:", i.name, "ID:", i.id, "Path:", i.path)
        
        return{'FINISHED'}

# select button
class CUSTOM_OT_selectAllItems(Operator):
    bl_idname = "custom.active_item"
    bl_label = "Print Active Item to Console"
    bl_description = "Print Active Selection"

    def execute(self, context):
        scn = context.scene
        print (scn.custom[scn.custom_index].name)
        
        return{'FINISHED'}
    
# Create custom property group
class CUSTOM_PG_items(PropertyGroup):
    # name: StringProperty() - instantiated by default
    id: IntProperty()
    path: StringProperty()


# -------------------------------------------------------------------
#   Registration
# -------------------------------------------------------------------

classes = (
    CUSTOM_OT_actionsUIList,
    CUSTOM_OT_blendSelect,
    CUSTOM_UL_items,
    CUSTOM_PT_blendFiles,
    CUSTOM_OT_clearListItems,
    CUSTOM_OT_printListItems,
    CUSTOM_OT_selectAllItems,
    CUSTOM_PG_items
)


def register():
    from bpy.utils import register_class
    for cls in classes:
        register_class(cls)
        
    bpy.types.Scene.custom = CollectionProperty(type=CUSTOM_PG_items)
    bpy.types.Scene.custom_index = IntProperty()

def unregister():
    from bpy.utils import unregister_class
    for cls in reversed(classes):
        unregister_class(cls)
    
    del bpy.types.Scene.custom
    del bpy.types.Scene.custom_index

if __name__ == "__main__":
    register()

Hi @dt192, updated the gist. You forgot to replace the assignment operators in the item group and to change the class names according to the current requirements in your fork hence the warnings in the console. Cheers