Thank you for your reply. Here is what I have done since to identify what is happening.
I deleted the flow and recreated it again hoping it would perform different simply because it is acting very strange. I am getting the same result.
The duplication appears to only be happening on the scheduled run not the test or manual run. I am still testing this theory to prove.
I am confident that I am using the correct internal SharePoint field name

As you can see here, the flow continues to create a new SharePoint record when one already exists for XX-12636.

It should not create but rather update as the filter is based on the SharePoint field and Excel field with the same data value.

I noticed the output shows it created a new record then updated the existing and new record. I proved this by adding 2 new SharePoint columns and entered values in the flow for created and update, so I know how the flow is behaving.

The records in SharePoint prove it appears to be creating and updating at the same time. Here is what is shown after one run of the flow.

The flow output shows it only updated the record:

Any thoughts??? I am lost on this one.