Dynamic Label in Title

Consider using SELECTEDVALUE DAX to capture the selection in a measure and then use it in your title.

Eg: In your case it would be something like:

Title of Sales Chart: "Top 3 Sales by" & SELECTEDVALUE(<Slicer Selection>)  

Title of Product Chart: "Top 3 Product by" & SELECTEDVALUE(<Slicer Selection>)  

You can use these measure in the title of the corresponding charts as a formula as below:

Based on field is your measure

For more details, refer below:

https://www.fourmoo.com/2017/08/01/power-bi-dynamically-changing-the-title-based-on-your-selection/