Selecting a document opens in both editors (Scrivener 3)

I want a binder document to open only in one of the editors, but at the moment, every binder document opens in both editors at the same time. Any suggestions?

My second question is related: How can I set up preferences, so that a link or a binder document to open in the active editor or copyholder?

This is set per-project, in Navigate > Binder Affects. The default is “Current Editor”, so you may have just switched it at some point by mistake in this project.

Thanks! Works great!