Hi,
I took a look at Outlook and Text Blaze gave me this selector for the sender:
{site: text; selector=.Q84Kk}
This is the full name including the email. If you want just the first name you can split it by " " and take the first item:
{=split({site: text; selector=.Q84Kk}, " ")[1]}
To see how the splitting works, look at this example:
{formtext: name=example; default=Joe Smith jsmith@example.com}
Full match: {=example}
First Name: {=split(example, " ")[1]}