As an employee I took the tactic of saying fuck it and saying what's on my mind. If it'll be used against me, so be it. I think that's the optimal path but it's not going to be everyone's cup of tea. At the end of the day it's on the employee to find their path out of this.

As a manager the best I can do is try to build a solid rapport with the person in hopes that they feel comfortable opening up. But there's no magic bullet to this and every person is different. That rapport also goes both ways. I struggle with newer employees as I have no connection with them and am much more likely to fall back on generic platitudes. As I get to know the person the questions I ask and suggestions I make can be more tailored to their personalities and comfort zones.

If an employee is having an issue that they don't want to put in writing (or you sense this), oftentimes a one-on-one is the only way to coax it out. Particularly if they have an issue with leadership, HR, other managers, etc. Decent managers are also using 1:1s to make sure their employees are treated well in the org as a whole.

But I recognize the 'decent' is doing some very heavy lifting in that sentence.