Dear Paul,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
I'm afraid that there is no way showing all content in a cell by hovering the mouse without clicking on it.
The only workaround may be to use the following example VBA to auto-convert the cell to comments.
Public Sub ValuesToComments()
Dim rng As Range
If TypeOf Selection Is Range Then
For Each rng In Selection.Cells
On Error Resume Next
rng.Comment.Delete
On Error GoTo 0
rng.AddComment Text:=rng.Value
rng.Comment.Shape.Height = 1000
Next rng
End If
End Sub

As our product developers are willing to hear feedback from users for product improvements, I kindly suggest you submit your feedback on the Feedback platformto convey your suggestions and ideas to the product developers directly so that they will know your requirements in your environment for further investigation.
Sincerely,
Cliff | Microsoft Community Moderator
***Note: In the event that you're unable to reply to this thread, please ensure that your Email address is verified in the Community Website by clicking on Your Account Name > "My Profile" > "Edit Profile" > Add your Email Address > tick "Receive email notifications" checkbox > click on "Save".***