The College Board has already released four digital adaptive SAT tests, one PSAT/NMSQT, and one PSAT8/9 in their Bluebook app. You can download it and start with the sample questions and try one test to get a baseline.
Woodlands Test Prep has a state of the art Digital Adaptive SAT practice engine with additional practice tests so students have access to additional, excellent practice.
Remember to pace yourself on the Bluebook tests and College Board materials. Test prep involves taking a test, seeing how it goes, identifying what you’d like to do differently next time, practicing those changes, and THEN trying a new test. Since we’re at the beginning of a new test format, official practice is less abundant than it will be in future years!