Three other family members and myself have at almost the same time and for completely different reasons became interested in or needed to become acquainted with image art of some form.
I wanted to find “The Tutorial” to share with everyone so we could relate bettter.
I haven’t come across a single tutorial that ‘unlocks’ GIMP for new users (if I’m reading your question correctly) but I’ve found Davies Media Design to be an excellent resource for video tutorials, both free and paid. Also Bernard Hooft has provided a free video course and book.
Be aware that lots of learning resources are being updated after the 3.0 release, so some tutorials may no longer be valid.