Look for courses taught by working scriptwriters, even if you're writing novels. Screenwriters are masters of economical character definition. A course I audited on Udemy, 'Character Development for Screenplays,' was brilliant at teaching how to define a character through action, visual detail, and a single line of dialogue that encapsulates their philosophy. Translating those techniques to prose, where you have more internal access, can give you incredibly sharp, cinematic characters. It trains you to make every moment of characterization pull double or triple duty.