To start out, I think you may be misunderstanding how the checklist works in it’s current form. It’s not designed to be used as a multiple select list to select items to submit elsewhere. Think of it more like to-do or a task list. Checking off a list item will immediately set a column value in that list sheet to true or false. Maybe you already understand that and I’m not understanding your app flow, but I just wanted to clarify.
I have a similar situation where I would like to create an invoice PDF per coach/student combination. I’m guessing it would require scripting, but I just haven’t gotten that far yet. For simplicity, I try to avoid scripting as much as I can. In your other post you mentioned that you had a checkbox to run the script. I wonder if a form button would be better. You could submit the user’s email and any other relevant info you need. Then maybe your script could use the additional info to only generate the PDF using the matching info from the form entry. The finally either delete the row or set a value in another column to indicate that the form entry has been processed and the PDF generated.