When a workflow and its steps are scheduled to run using the native scheduling in QuickConnect, there is no option to specify Quick Run or Full Run.
Quick Runs were implemented as a way to test Workflow changes in a more efficient manner. Full runs are always required for workflow runs to verify both the source and the target aside from using the mappings table in Quick Connect to discover items.
Does this mean that they always run in Full Run mode?
Yes, for scheduled run, it will always run in Full Run mode.
The cmdlet Start-QCWorkflow also lacks a Quick Run / Full Run option