I applied back in October 2019. Multiple stages of psychometric tests online (including situational, numerical, written, and video). The first test is pretty easy, it's not timed but try not to take more than 2 hours. Second stage was more challenging, it included a big written task to respond to an email, and also a video interview with an e-tray exercise, but if you've done your research (about EY and your industry) then that's not really that hard either.
Then the assessment centre, with loads of tasks (including group exercises, numerical test, written tasks, prioritisation tasks). You MUST have strong commercial awareness of current finance and technology trends. Also they monitor your behaviour all day so don't slouch, and maintain a cheerful disposition. I thought EY's assessment centre was much easier than the other Big Four's.
Partner Interview was very challenging for me. They give you pre-work a week in advance that you have to research and prepare a short speech type of thing for. Then they'll ask further questions about your topic. After that it blends into a regular interview with questions like 'what do you enjoy doing?', 'why tax/accounting?', etc. (it's a strengths-based interview so prepare accordingly).