There are plenty of STEM robots available for beginners. The MiniBalance ROS Ackermann Robot Car is made for serious developers. It comes with LiDAR navigation, Raspberry Pi brain, built-in PD controller, and everything you need to get started.
This robot has an aluminum alloy structure with 60mm wheels. It is smart enough to follow objects and people in any direction. It has a RGBD depth camera to measure the distance from objects in front of it. The companion app lets you view a live feed from the robot.