I am not aware of a way of creating pop-ups as you scroll across a spreadsheet - but I would be happy to be proved wrong.
As an alternative, I created a Text Box and using the Selection change event, the text in each cell is shown in the text box.
Create a new Text box, and check that it is named "Text Box 1", if not, change the name in the code to match.
Set the text box font to a larger size to 'magnify' the contents.
The following code displays the cell's text or concatenates contents if more than one cell is selected.
Here is the code which goes in the Worksheet object - Right-click the worksheet name and select View Code.
Paste this into the code window.
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim rngCell As Range
Dim strDisp As String
With ActiveSheet.Shapes("Text Box 1")
If Target.Cells.Count = 1 Then
.DrawingObject.Text = Target.Text
For Each rngCell In Target.Cells()
strDisp = strDisp & " " & rngCell.Text
.DrawingObject.Text = strDisp