Relative due date of subitem based on item date column

Hi, My company is trying to get setup on and while many things are fairly intuitive and are coming together easily, there are a handful of seemingly very basic project management processes that I just can’t seem to figure out how to automate here. Before anyone suggests integromat or zapier, please know that we are a small company, so paying for an external automation system on top of what we are already paying for is simply not an option for us.

My current hangup is on setting due dates; Specifically due dates on subitems that are relative to the item creation date or an item date column. something like:

“When item moved to board create subitem and set subitem duedate to item Date date plus some days”

This seems like such a simple and basic operation that I have to be missing something or not seeing an automation template somewhere? I could use a formula column for this, but we need these due dates to show on a calendar view and have notifications, which is not possible with the formula column to my understanding. Any guidance or help is very much appreciated.