I don't know as to your new question. I expect that the Navigation pane will always open as a Navigation aid rather than a Find aid; but the Find panel will open in response to Ctrl+F.

As I said, the safe mode was for diagnostics. You almost certainly have an Add-In that is causing this. Try disabling them all and see what happens.

See View, manage, and install add-ins in Office programs - Support.

If it works for you with Add-Ins disabled, try turning them back on, one at a time until you notice the problem again. Then you will know which one is the problem. Unless it provides some advantage you value over the Navigation pane problem, leave it disabled.

BTW, I find the navigation pane helpful enough that I assigned it a Keyboard Shortcut.