I put this mind map together a few years ago after a discussion about what a new VP of Engineering or CTO should think about in their first 90 days in a new role.
https://www.kartar.net/2020/07/vpe-and-cto-the-first-90-days/
https://www.kartar.net/2020/07/vpe-and-cto-the-first-90-days/