When you are experiencing a specific issue, here are the most likely places to check.
Some 2019 Cascadias shipped with a . If you see a small silver box zip-tied near the 7-way plug, this module fails often. When it fails, it mimics a blown fuse. Check for power into the module (from the truck) and out of the module (to the plug). No output means a bad module, not a fuse. 2019 freightliner cascadia trailer light fuse location
Find the fuse labeled for your issue (e.g., trailer markers). When you are experiencing a specific issue, here
Here is a diagram of the fuse box layout for a 2019 Freightliner Cascadia: 2019 freightliner cascadia trailer light fuse location