The Raspberry Pi platform is wonderful for learning Python coding. There are already plenty of STEM kits based on it. The SpiderPi is a Raspberry Pi powered AI robot that can handle color recognition, object tracking, obstacle detection, and visual line following. The code is open source.
This robot is based on the Pi 4B. You can control it with your PC or via your smartphone. SpiderPi has a high resolution camera with 2DOF rotation. It has a display to show the current battery voltage. It lasts up to 40 minutes on battery.