Drupal Developer Trio covers layout options and theming with Twig on Day 1, as well as basics for developing custom modules on Day 2 for anyone who already has a good grasp on Drupal site building. Each segment of the course is also offered as a separate unit for developers who may not need both frontend and backend instructions:

Layout & Theming
Module Development
If you need to brush up on site building, Promet also offers a 2-day Site Building course or a 5-day bundle that includes all three segments:

Site Building
Drupal Developer Immersion
Should I Take this Course?
The knowledge and know-how gained in this course is particularly helpful for:

Internal development teams who are preparing to migrate to a Drupal 8/9 website
Developers who are planning to build a new Drupal 9 website
Developers who are newly responsible for supporting a Drupal 9 website
Current Drupal Developers who are looking to firm up Acquia best practice knowledge for Drupal 9 Developer Certification
Recommended Experience
Experience with the following is required: 

Content authoring using a Content Management System
Familiarity with Drupal's administrative interface
Working knowledge of HTML and CSS