From ChatGPT that cited https://www.defensivedriving.org/dmv-handbook/right-of-way/

In a two-way stop scenario, right-of-way is determined by the actions of the drivers and not simply by who arrived first. Based on your description:

• The car across from you arrived first and is turning left, while you are going straight through the intersection.
• Generally, if you and the other car are waiting for traffic to clear, the car going straight (you) has the right-of-way once the traffic has cleared, even if the other driver arrived first.
• The car turning left must yield to oncoming traffic (you), unless you signal them to go first.

Despite this rule, many drivers incorrectly assume that arriving first gives them the right to turn left first. However, in this case, the correct order is for the driver going straight to go first, and the car turning left should wait until the intersection is clear.

It’s important to be cautious in these situations since some drivers might not follow these rules strictly.