Tesla could easily add proper blind spot warning but they are content let the highly inaccurate squiggly lines that half of us ignore, to be your blind spot warning. Hopefully they will wise up soon.
Lane Assist
Model Y monitors the markers on the lane you are driving in as well as the surrounding areas for the presence of vehicles or other objects.
When an object is detected in your blind spot or near the side of Model Y (such as a vehicle, guard rail, etc.), the touchscreen displays colored lines radiating from the image of your vehicle. The location of the lines correspond to the location of the detected object. The color of the lines (white, yellow, orange, or red) represent the object's proximity to Model Y, with white being the farthest and red being the closest and requiring your immediate attention. These colored lines only display when driving between approximately 12 km/h and 140 km/h. When Autosteer is active, these colored lines also display if driving slower than 12 km/h. However, the colored lines do not display if Model Y is at a standstill (for example, in heavy traffic).