C# Specflow+ How to run some code ONCE before the threads are created in .netcore for TestRail API

Question

I have written a Test Automation Framework in C# that uses Specflow with SpecFlow+ as the Runner.

I am using TestRail API to write the results to TestRail.

I want to create a new test run when I start the automation tests and then write all of the results to that test run.

So I have written some code using the

[BeforeTestRun]

hook to create a test run.

This works fine when I am running in single thread mode.

But when I run in multi-thread mode, a new test run is created for each thread.

How can I run some code that runs JUST ONCE before the threads are created to create just one test run?