To recap, if you would like to learn programming in PLC languages and testing them with Arduino this is a low budget step to do so.
On the website https://www.openplcproject.com/ is a good explanation on how to get started with your first project.
If you would like to test my code from my traffic light => You can download the map here: https://drive.google.com/drive/folders/1iv_ixV3rXCQ8M5idsQThI0uhB5TW6nyd?usp=sharing
If you want to open the project you have to select the entire map when selecting a file to open in the Open PLC editor.
If you want to upload it directly to the OpenPlc runtime you have to upload the file : "PLC_Runtime_traffic_light.st" included in the map.
*edit: answering the question: what is PLC? (printscreen from my post on Reddit)