I do not recommend starting off with a decision to use DynamoDB before you have worked with it directly for some time to understand it. You could spend months trying to shoehorn your use case into it before realizing you made a mistake. That said, DynamoDB can be incredibly powerful and inexpensive tool if used right.
Yea, probably, but it is especially true for DynamoDB because it can initially appear as though your use cases are all supported but that is only because you haven't internalized how it works yet. By the time you realize you made a mistake, you are way too far in the weeds and have to start over from scratch. I would venture that more than 50% of DynamoDB users have had this happen to them early on. Anecdotally, just look at the comments on this post. There are so many horror stories with DynamoDB, but they're basically all people who decided to use it before they really understood it.