I was just wondering if we have to post updates for our game
You don't have to!
It's encouraged - I do think having that external commitment is a good source of motivation - even if it's unknown faces that mostly won't acknowledge it, it tends to push you toward not disappointing people.
But some people in the past have found that counterproductive too, as they found themselves focusing too much on making something that'd look good on social media, and not enough on some longer features their games needed.
Bottom line - it's your decision, and probably depends a lot on your overall goals. But don't let pressure or fear of result make the decision for you :)
I'd further point out that "required" isn't really a productive way to look at this jam or anything about it; if you think of it that way and miss an update, you can start to feel like you've somehow failed.
Like you said, it's a good way to motivate yourself -- and, if you miss one, taking a more positive angle, like "well, better have a good one for tomorrow," can help avoid turning updates into some sort of slog or a source of anxiety.
For me, having a set of goals and then continually breaking each one down into tasks until any given task should take less than a day to accomplish helps avoid days where there's just nothing to talk about. It may not be much, but "my little dude/chick/alien/hamburger now actually faces in the direction it's moving" is progress, and progress is progress.