I have multiple spreadsheet bound projects, and I want once in a while run all of them together. Is there a possibility to automate this, as I do not want open each project and run it manually. And as I understand I cannot create installable timed triggers, as I have more than 20, and I am not collaborating with anyone.
My vision - is to create a standalone project where I loop through all the projects using their project/script key(id)s. I only do not know if this is possible, and if yes how do I code this - a call of a script knowing its scriptid?
In order to provide a proper response to the question, I'm writing this answer as a community wiki, since the issue was resolved from the comments section.
Yes, it's possible to run several projects at once with Apps Script with method scripts.run
You can use this example to have an idea on how to do it with Apps Script.
The documentation that @Ruben shared above has specific details to accomplish what you're looking for. Make sure to check the requirements and also the limitations to check if the projects you're trying to run meet the requirements.