A script can be marked "Run on start" during save:

Then when the Microcontroller Brick is next powered on, that script will be automatically run. This lets you create autonomous projects that are not tethered to the PC.

A script that is marked as "Run on start" is displayed as red and bold in the "Open" dialog:

Only one script can be marked "Run on start" at any time. If a new script is saved with "Run on start", it will replace the status of the previous script.

To remove the "Run on start" status of a script, simply save it again with the checkbox unchecked.

Implementation notes

The name of the script to run on start is stored in a file called /rbx/.autorun in the ESP32's flash memory.