尝试

Sub telegram_pruebas_photo()

    Const URL = "https://api.telegram.org/bot"
    Const TOKEN = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
    Const METHOD_NAME = "/sendPhoto?"
    Const CHAT_ID = "-xxxxxxxxxxx"
    
    Const FOLDER = "C:documentsSCREENSHOT"
    Const JPG_FILE = "picture1.jpg"
    
    Dim data As Object, key
    Set data = CreateObject("Scripting.Dictionary")
    data.Add "chat_id", CHAT_ID
    
    ' generate boundary
    Dim BOUNDARY, s As String, n As Integer
    For n = 1 To 16: s = s & Chr(65 + Int(Rnd * 25)): Next
    BOUNDARY = s & CDbl(Now)

    Dim part As String, ado As Object
    For Each key In data.keys
        part = part & "--" & BOUNDARY & vbCrLf
        part = part & "Content-Disposition: form-data; name=""" & key & """" & vbCrLf & vbCrLf
        part = part & data(key) & vbCrLf
    Next
    ' filename
    part = part & "--" & BOUNDARY & vbCrLf
    part = part & "Content-Disposition: form-data; name=""photo""; filename=""" & JPG_FILE & """" & vbCrLf & vbCrLf
    
    ' read jpg file as binary
    Dim jpg
    Set ado = CreateObject("ADODB.Stream")
    ado.Type = 1 'binary
    ado.Open
    ado.LoadFromFile FOLDER & JPG_FILE
    ado.Position = 0
    jpg = ado.read
    ado.Close

    ' combine part, jpg , end
    ado.Open
    ado.Position = 0
    ado.Type = 1 ' binary
    ado.Write ToBytes(part)
    ado.Write jpg
    ado.Write ToBytes(vbCrLf & "--" & BOUNDARY & "--")
    ado.Position = 0

    Dim req As Object, reqURL As String
    Set req = CreateObject("MSXML2.XMLHTTP")
    reqURL = URL & TOKEN & METHOD_NAME
    With req
        .Open "POST", reqURL, False
        .setRequestHeader "Content-Type", "multipart/form-data; boundary=" & BOUNDARY
        .send ado.read
        MsgBox .responseText
    End With

End Sub

Function ToBytes(str As String) As Variant

    Dim ado As Object
    Set ado = CreateObject("ADODB.Stream")
    ado.Open
    ado.Type = 2 ' text
    ado.Charset = "_autodetect"
    ado.WriteText str
    ado.Position = 0
    ado.Type = 1
    ToBytes = ado.read
    ado.Close

End Function