Most of the online tests are very similar, and test the same skillset. It´s a good thing, since you can prep for them with a very unified approach. Although this may not seem so at first sight since the formats may differ, what is important here -as well as when solving cases- is the core skillset they are tryng to test. This is common, and the most important skills are:
80-20 analysis: capacity to analize, interpret and extract conclusions quickly and in a agile way from a ton of data -of which not all is useful-
Analytic and critical thinking: many ways tested with graphs, charts and tables, that you need to understand and derive decisions or insights from
Mathematical skills: are always somehow present, for which you need to be fast int he basics
The way to get better is practicing as much as possible with similar exercises -those targeted at the same skillset-. Hence, I would strongly recomment you practice it with the Integrated Reasoning part of the GMAT exam.
There are free exams in the internet that you can use for practice (the one of LBS MBA page, Verits prep, as well as some free trials for courses such as the one of The Economist (https://gmat.economist.com/)
Furthermore, you can leverage the MBB tests (https://www.myconsultingoffer.org/case-study-interview-prep/bcg-online/, https://www.psychometricinstitute.co.uk/Free-Aptitude-Tests.asp, and many others)
Hope it helps!