Hi there @bastian and welcome to the forum!
There is a similar blog post here and another one with potential alternative solutions if the addrow doesn't work for you here.
In any case, the auto-incremented ID will not be added until you run the upsert query.
You can have two different actions in your save button, one conditioned to where newRows is not undefined/null that will insert the new record, one for changesetArray which will edit the changed records.
Hope this helps!