Received a question about this notification/error/pop up. This is simply informing you that the regular market session has ended (a.k.a. the closing bell). Although data may still be coming in and the market may allow for trading, the bars on the chart will not update anymore.
You have the choice to update the chart to show data outside of regular hours.
I personally check the box “Do not display this message again” since I do not need to be reminded every day that the market closes… every day.