"Always be ready to leave"

Big yes

"For a year before leaving, I talked openly with my supervisor and HR about my dissatisfaction"

Big, big, big no. Might have worked for OP this time but in general this will backfire drastically. In many European countries this can even reduce the usually robust protections you have as an employee.

Indeed. I _have_ been able to (mostly) talk about things that I was dissatisfied about, but out of dozen bosses I had, that was with only two. I wouldn't trust the others to start looking into a replacement the moment I gave even a hint of dissatisfaction. For some others, I could express disagreement about outcomes or company policies, but in some cases even pushing too much on those topics can get you fast tracked out. I have seen it happen.

To be able to have (again, mostly) honest conversations with a boss or HR is a privilege. In 99% of the cases, HR is there to protect the company, there were only a handful of HR employees that went above and beyond. And even then, you had to make sure not to use some triggering words. I mean this in the literal sense, there are a few things that, if you say, that triggers an automatic HR response, regardless of who you are talking to. Hinting of leaving, even with an unspecified timeframe, is one of them.

In general, don't do this.

Also, exit interviews cannot benefit you. Decline.

> In many European countries this can even reduce the usually robust protections you have as an employee.

Huh, where?

> In many European countries this can even reduce the usually robust protections you have as an employee.

Which countries specifically?

It completely depends on the management. Be sure to know them.