Do I need to not worry at all about how my partitions are set then?
With constantly evolving services like DynamoDB, I think we have to design the best we can using our intuition and then test the heck out of it. Dynamo is one of those core services that evolve very quickly–much more quickly than the documentation or the exam can be updated. I can say that I have first-hand run into the limits of Dynamo despite what 2018 or 2019 blog posts say. Might have been a fluke or some temporary issue, but there is what AWS intends and how it actually performs.
I would still design with the partition limits in mind if it doesn’t force you to do anything crazy. The official Best Practices page in the AWS docs still talk about all the same partition limitations and was last updated this month.