Going to need a bit more info than just that!

Can you add an example worksheet, with an expected outcome?

Purfleet

You need to use the MAXIFS function and convert your data into a table so you can use structured references rather than address entire columns.  See attached workbook.

TextBox1.Value = Application.WorksheetFunction.MaxIfs (Range("Table1[Value]"), Range("Table1[Type]"), ComboBox1.Value)

These posts may help with your userform https://www.myonlinetraininghub.com/tag/userforms

Regards

Phil

You can make the range Dynamic in the code.

Private Sub ComboBox1_Change()
Dim rng As Range, x

Set rng = Range("A1:A" & Cells(Rows.Count, "A").End(xlUp).Row)

x = Application.WorksheetFunction _
.MaxIfs(rng.Offset(, 1), rng, Me.ComboBox1)

If x > 0 Then
Me.TextBox1.Value = x + 1
Else
Me.TextBox1.Value = 1
End If

End Sub