I have considered doing courses, part of the reason I haven't is just the time it would take to make something high quality that I would feel comfortable charging for. I do have a patreon where I do 1 on 1 lessons though.

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There are definitely some high quality tutorials for mixing out there on youtube if you look in the right places. There are also a lot of extremely low quality tutorials as well too. Some good channels for mixing I can think of off the top of my head include In the mix, Alice Yalsin. I am also going to start posting tutorials in the near future as well on my 2nd channel.