Fritz 17 settings quesiton

Quick question: how the heck do I set it so that in the notation panel new moves overwrite old ones, instead of inserting new lines?

If it works the same as all the others I know, you can't. You first track through your main line, then if you backtrack and play a different line, that is a variation, not the main line.

You enter a new move and it's a new variation. If you want that variation to be a new main line, then you have to "promote" it.

In Arena it's a setting. You can let it automatically overwrite if you wish to.