Question How can I learn sci Fi VFX?

While Sci-Fi Muzzle Flash tutorial might not exist yet on YouTube, I would say that the technique involved are the same as for any muzzle Flash VFX. And it's going to involve a mix of, modeling , Uvs transform, Shaders, texturing and particles.
You first need to have a clear idea of what your muzzle should look like. Muzzle are a key important to game feel and often convey a lot of information in regardszs to the weapon in use. So make some research, gather references that suit you or maybe try to draw some quick concept.
Based on the weapon, this should help you to answer the basic questions like:

-Size of Muzzle ?
-Color of the Muzzle ?
-Shapes?
etc..

With a clearer idea in mind, you should then be able to decompose your VFX in the different core elements that are needed :
ex: Core Muzzle, Flash, Sparks, Bullet ejections?, Smoke lingering? Impact decals?

So, gather references from Sci-Fi movies, games, anime, comics, and learn how other Muzzle flash are made in games.
Even if they're not Sci-Fi, the techniques won't be different. The shapes, Colors, feels will be different but that's all.

That being said, you're in luck because I've in memory a great GDC 2023 talk by Shen-Ming Spurgeon and Matt Christopherson about the VFX of Callisto Protocol. And, lucky you, they are talking about their Sci-Fi Muzzle flash and weapons: First concepts and different iterations to achieve the final Muzzle flash of one of the main weapon. While you need a subscription to see the videos, you can access the PowerPoint presentation for free.

It's starting page 35, and it's a great talk about how to develop VFX thought visual iteration and through communication with the Game designer. Page 59, there's also a nice chapter to “push” the Sci-Fi feeling of a weapon. With Free access it's missing the videos, but still I'm sure that you'll be able to get some good information out of it.
GDC 2023 :Navigating 'The Callisto Protocol''s VFX

So, between this and the muzzle flash tutorial online, I hope that you'll come back and show us some delightful SCi-Fi VFX.
Don' t hesitate to share your WIP and progression on the Unity Discord server.
Have a great day.

 

Also, after looking more closely at the video you provided, I've noticed that this is coming from a VFX pack on the asset store. So after looking at Muzzle flash VFX tutorial, and the GDC talk that I linked to you, if you can afford it, I would suggest that you simply buy the asset from the store. This would allow you to inspect each VFX and assets. By inspecting and trying to understand how and why the assets (VFX, Textures, meshes, Shaders) have been done this way, by trying to reproduce them from scratch you could learn a lot from this experience.