A little late to the party, but I just passed the latest Strategy Designer exam. Since it's a really new one (about one week old), there isn't much guidance about it yet. I'd like to share a few tips during my preparation.
Exam Guide
https://trailhead.salesforce.com/help?article=Salesforce-Certified-Strategy-Designer-Exam-Guide
This is the most important page to understand the exam, a few things to note:
The passing score is 70% (a little higher than usual). The portions on design concepts are very high (Value Design 32% and Intagiible Deliverables 26%).
Preparation
https://trailhead.salesforce.com/users/strailhead/trailmixes/prepare-for-your-strategy-designer-credential
https://trailhead.salesforce.com/en/users/salesforceexperience/trailmixes/salesforce-design-strategist-career
These are the 2 Trailmixes provided by Trailhead, and the first one is tailored to the exam guide. However, it can take a while to complete. If you're in a hurry, the second one should equip you with enough knowledge about the content tested in a short time.
The core is Learn Strategy Design
https://trailhead.salesforce.com/en/content/learn/trails/get-started-with-design-strategy
By doing this tail, I refreshed a lot of knowledge with proper concepts. I've been using some of the methods mentioned in my daily job but didn't know their names and details. This tail provides the concepts, best practices together with a fictitious example of Cloud Kicks' supply chain challenge. It's a delightful learning journey for the Strategy Design concept.
Final Thoughts
This exam is focusing on design, and everything related to it, such as concepts, frameworks, and techniques. You barely get tested on your Salesforce technical knowledge, but it's great complementary to that. I think if you're doing any sort of design jobs in Salesforce projects, this is a cert worthy of the effort.
