Absolutely. But it's also a question of what you want to optimize. Is it more about making sure you keep your current job, is it about maximizing income or is it about having peace of mind?

First, figure out what is the probability of you being able to find a new job. For most developers that are reasonably good, in the current market, finding a new job of at least the same compensation (probably more!) is possible, if not easy.

Assuming the calculation from the previous item goes well and if you want to optimize for peace of mind, say what you feel. If it turns out you have a bad manager, start looking for a new job. Getting fired immediately in the situation described in the original comment is extremely unlikely. If you get the impression that things are not going as expected, start looking for a new job.

If you want to optimize for keeping the current job and not for peace of mind, yes, technically the safest way for now is keep doing what the original poster said. However, how long can you keep that up? How bad will it make you feel to keep faking?

Also, it's very common to over-estimate the likelyhood of extreme edge cases happening. They are possible, but need to be weighted with the likelyhood and the risk. Again, if you are fairly certain that you can get a new job if needed, then the risk is small and the likelyhood (as you mentioned) is low. However, the peace of mind change can be substantial. To me it seems worth it. Maybe to you it wouldn't be. Then yes, don't do it. But it's important to think of all the factors and not just focus on not rocking the boat. Sometimes risks are worth taking. Sometimes not. Life's complicated and you only get one go at it :)

It’s always in my best interest to tell my manager that I don’t want to get promoted.

If I don’t tell him and they surprise me with a promotion, that’s not a great outcome. I know I’m a horrible people manager (did that for one horrible year). But I’m pretty good with managing projects.

If I do tell him and he forces it on me anyway or I can tell that’s not what he wants to hear, I need to know that and be prepared to change jobs.

But then again, I enjoy coming in fixing a problem, training, and “putting myself out of a job”. That isn’t exactly the model of someone who is interested in career progression at one job…