Executing a form automation
The System app has an "execute automation" action that can be used for one automation to execute another automation:
But when the executed child automation contains a form, that child automation must be turned on in order for form submissions to be processed.
To do this, use the "executed by automation (instant)" System app trigger:
Now the child automation can be left turned on so its form(s) will receive submissions and the child automation will only perform processing when executed by its parent automation(s).