I understand the reason is to prevent spam and bad answer, but is there any workflow to still submit an answer and get the reputation for it?
Or do I simply have to write a comment and go away without any reputation. (You can also ask someone in chat if you have the 100 rep bonus to submit an answer for you, but you don't gain any reputation either)
10 reputation (which is how much you need to answer a protected question) really isn't that much. That is a single upvote on an answer, 2 upvotes to a question or 5 accepted edit suggestions (or some combination thereof)...
If you havn't earned 10 reputation on the site there's a good chance you don't know the site well enough to post a good, high quality quality answer, and that's exactly what protecting a question is for (it's not just about spam, but general low quality answers too).
You already stated the goal of protected question, so there's no real workaround on this protected question specifically.
That said, you need only 10 points, as explained in this blog post, so you can:
And that will be enough to be able to add your answer to this protected question.
Just because you're an expert on one site does not make you an expert on every single site.
I have somewhat high reputation on superuser.com. I however shouldn't be trusted on say, parenting or SO based on that. The minimum reputation doesn't include that for that reason. In fact, this was a change made somewhat later specifically because people with association reputation bonuses were posting questions that were not that good.
It is absolutely and completely by design. You might have luck, very politely asking a moderator if they could undo the protection on the question, or just spend the minimal effort getting that 10 reputation on the site.
