Hello,
I've just had a look at the video, and not a newbie error (and I have to say I'm confused now).
I've just done something very similar in one of our apps, and it was the Default property I set to (in this case) ThisItem.Description, and it's the .Text property I used to access the value in order to save it (or rather, update the collection from the OnChange property, in this app).


Certainly, in the version of PowerApps I'm using, Text Inputs don't have a .Value property, and while Microsoft does like to make sudden changes, this would be quite a drastic one.