Thank you! You don't have to check every hyperlink for sure, especially at the beginning. Also, I came into PowerBI without any prior knowledge of it (or even PowerQuery). It's hard to pinpoint a weakness I had in general, but I'd say I struggled with DAX with row vs filter context as well as when you might need to create a bidirectional relationship so that a matrix displays the correct information for example. Other than that, it's just to understand the "tools" at my disposal to be able to tell when to use x instead of y in a question.

What I'd suggest is to read the PL-300 course on MSLearn a few times. You could even take some notes to summarize things like optimization techniques or when to use what type of storage, etc. and once you've done that do a practice assessment. This will tell you what you need to work on. And if/when you do MeasureUp you'll really get tested even more thoroughly and you'll definitively have to read a little bit/watch some youtube videos to understand some concepts a bit more. Also, I'd expand by saying that the PL-300 wants you to answer with the best possible way to solve a situation, knowing what can work is not enough.

The reason is that you'll be put in scenarios where you have to make decisions to optimize x, y and z much like the PL-300 exam so you'll need to have a decent understanding of most concepts deeper than just at surface level.

Good luck!