> how do you agree with something you don't agree with?

This is your real question, I think. And there are different answers here based on who you are and the role you have at within the company.

First off, I strongly recommend a policy of "never lie". I don't care what the situation is. People are natural lie/bullshit detectors, the truth always reveals itself. Once you lose trust getting it back can be near impossible to do. And most industries are "small" in that word gets around quickly. Just don't do it.

Next, we'll ignore decisions you disagree with that can be considered insider information. Those are as simple as the equivalent to "no comment" or just blatantly ignoring the question and removing yourself from the environment.

Finally, there are three situations remaining:

1. You disagree and are a decision maker (others will be looking to you for answers and leadership)

2. You disagree, are a decision maker, but are letting the team under you make the call.

3. You disagree but are in a simple IC role, perhaps lending thoughts or ideas into the discussion, but play no role in the decision making itself.

If you're a decision maker just be honest. If necessary, outline the problems, the proposals, where (your desired) proposal fell short or why it was rejected. Outline what was liked about the accepted decision, etc. Also take the time to state where the accepted decision may fall short and plan for those contingencies. It's not a zero-sum game. If the decision is from on high, never have the attitude of of "we're taking one for the team" as opposed to "leadership recognizes that we can manage the difficulties that may ensue, but <other teams> will benefit exponentially more because of this choice". If the decision is from those under you, be supportive. Have regular check-ins to make sure your concerns are being addressed and be a cheerleader for them. Understand why they made their choice. What problems did they see that you didn't? etc.

If you're just an IC (or even a decision maker accepting a decision from on-high), you have to ask yourself "is this the hill I want to die on?" Does it really matter if we use Ruby instead of Haskell? If the company doesn't allow hybrid or remote work? Only you can answer these questions for yourself. If you really care and have made that known, then start looking for other employment. If not, then when someone asks, tell the truth: you disagree, this is why, but there's things at every job that will be problematic and this - in the grand scheme of things - is minor, not worth fussing over, and then note (also for yourself) the positive aspects of the decision for the greater good of the company.

Also, I'd like to bring up one other thing you didn't ask about, but can be important. It's possible that you don't care too much about the decision made, but very much care about the reason(s) why as they may be a fundamental indicator of future decisions you will care about. When those happen, bring them up appropriately and early. If they aren't addressed, start looking elsewhere or - in my experience - your life will end up miserable. But a great boss will address them and may even be happy/surprised.