101 Voice training
this video helped me a lot, and was my primary reference when starting out with voice training, strongly recommend
I had almost forgotten about Stef, because I had started watching around the time of her transition. She's really good at explaining her journey, but I haven't watched her channel in over 5 years.
Yeah, her channel fell off after she stopped posting for a while, but I found a lot of her content invaluable back when it was fresh.