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LINQPad 8 supports only .NET 3.1 and later, i.e., .NET Core 3.1, 5, 6, 7, 8, and 9.

For .NET Framework 4.x support, you need to download LINQPad 5.

Do you have C# preview features enabled?

Sounds like https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/first-class-span-types#calling-reverse-on-an-array

The static ToDump method applies to scripts and My Extensions - not drivers.

With drivers, you instead override the PreprocessObjectToWrite method. This is described in the documentation:
https://www.linqpad.net/Extensibility.aspx

Also, change the Language in the dropdown to 'C# Statements'.

Or else wrap your code in a void Main():

void Main()
{
    IWebDriver driver = ...
    ...
}

What is this type? Where it came from? Are you sure it is not delay loaded?

Please provide minimum working example.

IWebdriver has no relation to LINQPad. It's part of Selenium.

Since broken collection Mysql is selected script fails on startup.

Change connection (at the top right) to none

I don't have 'Microsoft.ACE.OLEDB.12.0' on my machine, so I can't test this properly but looking at the files included in Helper.7z you have two copies of System.Diagnostics.PerformanceCounter.dll and one of them is a lot smaller and the constructor in CounterCreationData is

    public CounterCreationData(string counterName, string counterHelp, PerformanceCounterType counterType)
    {
        throw new PlatformNotSupportedException(System.SR.PlatformNotSupported_PerfCounters);
    }

whereas the other is

    public CounterCreationData(string counterName, string counterHelp, PerformanceCounterType counterType)
    {
        CounterType = counterType;
        CounterName = counterName;
        CounterHelp = counterHelp;
    }

So the smaller looks like a non-windows version and being used by LinqPad whereas the latter is the windows version.

Not sure of the exact reason by LinqPad picks the wrong dll but I suspect it is related to the shadowing where it attempts to copy all the necessary dlls to a shadow folder and runs from that folder.

I suspect if you delete this non-windows dll from your Helper\bin\Debug\net9.0 folder, then LinqPad will work.

Not sure how you are supposed to tell which is the correct version as the version numbers are the same.

Sounds like your project has global using directives or the project file has <ImplicitUsings>enable</ImplicitUsings>.

Create a LINQPad script with the following content:

global using System;
global using System.Linq;
global using System.Collections.Generic;
global using System.IO;
global using System.Net.Http;
global using System.Threading;
global using System.Threading.Tasks;

and save it to a file such as "implicits.linq". You can add any other imports that your project needs. Note that this script must have the language set to "C# Statements".

Then in your main script, include this script as follows:

#load "implicits"

It would be nice to have some kind of directive, kind of #LINQPad hide_on_run+, to hide code window when running. I have an Avalonia application for which I don't need to see the code at all.