I would like to split all words in my cell by Uppercase, an example:
Original values:
MikeJones
RinaJonesJunior
MichealSamuelsLurth
Having acknowledged Excellll's remarkable formula, the most efficient code solution would be RegExp based. This avoids long loops.

Function SplitCaps(strIn As String) As String
Dim objRegex As Object
Set objRegex = CreateObject("vbscript.regexp")
With objRegex
.Global = True
.Pattern = "([a-z])([A-Z])"
SplitCaps = .Replace(strIn, "$1 $2")
End With
End Function