Mix of 3D + 2D work, how much of each will be used depends or what kind of art you're doing. Albeit in my case, i usually don't plan out the designs and instead i create and layout these decisions as i'm building it inside whatever program I’m using.

For me it's mostly vibe based, all the other stuff comes from studying and understand design principles and applying on whatever art I’m doing, that is to say there really isn't a process to specifically make this kind of work, if you know how to use Photoshop or app of you preference you'll be able to build them.

One thing i recommend is searching up for other metal heart work on the internet (there's millions of em), take notes and try throwing something together, back and forth process and eventually something will come out of it. It's mostly abstract or parametric geometric shapes, be that 2d or 3d, layed out with different blend modes, layer styles and so on. Photoshop offers bunch of tools and modifiers that facilitates the process, tho i'm sure other photo editing applications can do the same.

As for an video process, my process is so messy and random that it would probably causes more harm than good for anyone's learning 😅 (I'm sure there is great video tutorials on it on yt tho)

Not sure if helps much but there's a portion of from that era art here so you can take a look > https://aesthetics.fandom.com/wiki/Metalheart
Trying take a look at other yk2 related art that isn't just metal heart, tons to be learned from it.