What you are looking for is definitely possible, although will require some slightly advanced techniques.
Essentially what you are looking for here is a “form within a form”. Not possible with the native form options that come out of the box with Glide, but can be done by leveraging a custom form. I recently built a copyable concept App for somebody else looking to do a similar thing. You’re welcome to make a copy for yourself and study it to see how it’s done.
Again, this will be possible, but if the number of rows to be added is variable - and it sounds like it will be - then you’ll probably need to use something external to Glide. Either some Apps Script (if you’re using Google Sheets), or an integration tool such as Zapier or Make. If your project is based on Glide Tables only, then you’ll need a subscription plan that includes API access (Pro or above).
I’d probably be exploring options for minimising the number of rows to be used. If the tasks are date based, then it might be possible to set it up in such a way that each set of tasks only occupies a single row. Difficult to say without understanding in greater detail.