Add-in with C#

To create a VBE add-in for the Visual Basic Editor you can use C#.
Create a [[COM Add-in]] that implements the IDTExtensibility2 interface.

Creating

Open Visual Studio 2022 as Administrator.
New Project, Visual C#, Windows Desktop, Class Library (.NET Framework).
Change the Name to "VBACOMAddin".
Change the Location to somewhere on your C drive.
Check the .NET Framework version is correct and press OK.
Rename the Class1.cs file to MyConnect.cs.
Add four references to this project, (Project > Add Reference).
(1) Assemblies, Extensions: Microsoft.Vbe.Interop
(2) Assemblies, Framework: "System.Windows.Forms"
(3) COM, Type Libraries: "Microsoft Office 16.0 Object Library".
(4) COM: "Microsoft Visual Basic for Applications Extensibility 5.3" (VBIDE)
(5) : Microsoft Add-in Designer (Extensibility)
Remove the default class.
Add the following class underneath the interface in the MyConnect.cs file.

namespace VBACOMAddin1 
{ 
    [System.Runtime.InteropServices.ProgId("VBEAddin.MyConnect")] 
    [System.Runtime.InteropServices.Guid("0B58C36E-DE4E-4C40-8ED2-960437BFB7B1")] 
    [System.Runtime.InteropServices.ClassInterface(System.Runtime.InteropServices.ClassInterfaceType.None)] 
    [System.Runtime.InteropServices.ComVisible(true)] 
    [System.Runtime.InteropServices.ComDefaultInterface(typeof(Extensibility.IDTExtensibility2))] 
    public class MyConnect 
    { 
        public Microsoft.Vbe.Interop.VBE _ApplicationObject; 
        public Microsoft.Office.Core.COMAddIn _AddinInstance; 

        public void OnConnection( 
            object Application, 
            Extensibility.ext_ConnectMode ConnectMode, 
            object AddInInst, 
            ref System.Array custom) 
        { 
            this._AddinInstance = (Microsoft.Vbe.Interop.VBE)Application; 

            var wordApp = Application as Microsoft.Office.Interop.Word.Application; 
            this._AddinInstance = wordApp?.VBE; 

            if (this._AddinInstance == null) 
            { 
                this._AddinInstance = (Microsoft.Office.Core.COMAddIn)AddInInst; 
                this._AddinInstance.Object = this; 
            } 

            System.Windows.Forms.MessageBox.Show("onConnection"); 

            AddMenuButton(); 

            System.Windows.Forms.MessageBox.Show("Menu Button added"); 

        } 
        public void OnDisconnection( 
            Extensibility.ext_DisconnectMode RemoveMode, 
            ref System.Array custom) 
        { 

            this._AddinInstance = null; 
        } 
        public void OnAddInsUpdate(ref System.Array custom) 
        { } 
        public void OnStartupComplete(ref System.Array custom) 
        { } 
        public void OnBeginShutdown(ref System.Array custom) 
        { } 

        private void AddMenuButton() 
        { 
            Microsoft.Office.Core.CommandBarButton button; 

            Microsoft.Office.Core.CommandBars bars = 
              (Microsoft.Office.Core.CommandBars)_VBEInstance.CommandBars; 

            Microsoft.Office.Core.CommandBar menuBar = bars["Menu Bar"]; 
            Microsoft.Office.Core.CommandBarControl toolsMenu = menuBar.Controls["Tools"]; 

            var popup = (Microsoft.Office.Core.CommandBarPopup)toolsMenu; 

            button = (Microsoft.Office.Core.CommandBarButton)popup.Controls.Add( 
                Microsoft.Office.Core.MsoControlType.msoControlButton, 
                Temporary: true); 

            button.Caption = "My VBE Add-in Action"; 
            button.Tag = "MyVbeAddinButton"; 
            button.Style = Microsoft.Office.Core.MsoButtonStyle.msoButtonCaption; 

            button.Click += 
               new Microsoft.Office.Core._CommandBarButtonEvents_ClickEventHandler(Button_Click); 
        } 

        private void Button_Click(Microsoft.Office.Core.CommandBarButton ctrl, 
                                  ref bool cancelDefault) 
        { 
            System.Windows.Forms.MessageBox.Show( 
                "Button clicked inside the VBE.", 
                "VBE Add-in"); 
        } 
    } 
} 

Make sure the Guid Id is replaced using (Tools > Create GUID).
Select Build > Build Solution).
At this point no registry entries are added to the registry.
Select (Project > Properties).
Display the Build tab.
Tick the "Register for COM Interop" checkbox (requires admin rights).
Close the Properties window.
Select (Build > Build Solution).
When the solution is built a "TLB" file appears in the "\bin\Debug\" folder.
When the solution is built the RegAsm tool automatically runs.
The RegAsm tool adds the necessary class and interface information to the registry.

C:\Windows\Microsoft.NET\Framework\v4.0.30319\ RegAsm /codebase VBACOMAddin.dll 

Registry Keys - COM Add-in

Microsoft Office COM add-ins are identified by reading from the registry.
You can view the registry by going to the Windows start menu, choosing Run, typing regedit and pressing OK.
There must be a key representing the COM Add-in under the Addins key:
64 Bit Office - HKEY_CURRENT_USER\Software\Microsoft\VBA\VBE\7.1\Addins64\
32 Bit Office - HKEY_CURRENT_USER\Software\Microsoft\VBA\VBE\7.1\Addins\

HKEY_CURRENT_USER\Software\Microsoft\VBA\VBE\6.0\Addins\VBACOMAddin.MyConnect 
HKEY_CURRENT_USER\Software\Microsoft\VBA\VBE\7.1\Addins\VBACOMAddin.MyConnect 
(String)(Default) - (value not set) 
(String) Description - VBA COM Addin 
(String) FriendlyName - VBACOMAddin 
(DWord) LoadBehavior - 3 

Description - A brief description of the add-in.
FriendlyName - A user friendly name that is displayed in the COM add-ins dialog box.
Load Behavior - The load behaviour of the add-in.

Manually run the registry

Visual Basic Editor

(Tools > Addin Manager)