To check your direct report's performance trend, open their 1-on-1 meeting. Scroll down to the Private Notes section.
Once you see the trend, you can hover over the graph points to view more details. This performance trend as well is only visible to you. Here's a video to help you understand the process better.
https://drive.google.com/file/d/1urI2bu8DfjO-Pk3GjUx0BUi1dWForrQj/view?usp=sharing