No, there is no such constant {dotnethighestavailable}
. It would be useless anyway because you need to consider that not always you will have the latest Inno Setup release which would reflect the most recent .NET framework.
If your question has been raised because you are missing a {dotnet45}
constant, then I would refer you to this post
, where is written that .NET 4.5 framework is in the same directory as .NET 4.0 and so you can use the {dotnet40}
constant.