I would highly recommend checking out VFX Apprentice. I didn't know of them when I was learning sadly, but all the artists I see that learned from them have incredible timing and general vfx skills. If you have any other questions you can DM me :D.

Hi I am an Associate VFX Artist, I just got my first job in game dev. And if you go for RT-VFX I would recommend having a sample of the basic elements (fire, water, earth, etc). Also having a polished explosion is always good.