I've always read that hiding the "Add new" button from the subforms was not possible, even with online help. I even searched the forum and they say it can not be done. (Hope I was wrong)

I show you how I found a way to hide it with a simple ruler.

1. In automation, create a new task:

2. Create a new ruler:

Result subform:

If they already have it in good time. Otherwise I hope you find them useful.

Note: I am also coultando the "X" that deletes a row.

Greetings from Cusco - Peru.