The SqlHelpers class does not exist in .NET (Core). The last version of .NET that supported it was .NET Framework 4.8.1.
The class name was "SqlHelpers", not "SqlHelper".
AFAIK, there is no equivalent in .NET 8.0.
I suppose you can go to the .NET Reference Source and get the source code for the SqlHelpers class and just make it yourself.
Reference Source - SqlHelpers[
^]. Of course, you'll have to make some changes because your source won't have all of the build infrastructure the Reference Source has, like a custom Errors class.