The online tests across companies are very similar

Format? Somewhat. Content and what's required from you ability-wise? Not at all.

The best way is to really find online tests / questions and practice. Regardless as to whether is a new or old test, the principles are mostly the same:

• Time management (need to think quick)
• Business knowledge/context (incl key formulas)
• Critical thinking (answers that are very similar to each other...clues "hidden" in the text)
• Ability to interpret data/charts

Think of it as a merge of a case and the GMAT/GRE.

You need to be clear on some key case-related and account formulas (margin, growth, breakeven, etc) as well as be good at critically understanding the question (including nuance to questions) and parsing through complicated text with a fair amount of distraction.

You'll also need to be good at chart/graph reading.

The (old) McKinsey PST, BCG Online Test, Bain SOVA test, etc. are all quite similar so leverage resources across all of them.

https://www.myconsultingoffer.org/case-study-interview-prep/bcg-online/

https://www.shl.com/shldirect/en/practice-tests

https://www.psychometricinstitute.co.uk/Free-Aptitude-Tests.asp

Which position are you applying to? I've applied to OW in Singapore for an entry-level position and was just asked to do a hirevue video interview but not PST.