I need help! How is this technique called?

I've had this open in Photoshop since earlier today, and I suddenly remembered where I have seen this effect before.  It was a big thing 10 - 15 years ago using camera movement and slow shutter speeds.  Especially with Nikon DSLRs that could do double exposures.  I don't think this is a double exposure because there is some masking involved — you'd have no control doing it all in-camera.   You can try motion blur, but IME you can't get the same look.  What you do need to do is add noise to give the motion blur something to work on.  Make the layer a Smart Object (a total no brainer) and you can keep changing the settings to home in on it.  Unsharp Mask is better than Smart Sharpen for this, as the latter creates nasty halos when pushed to the extents you'd need for this.  I am still leaning towards it involving at least one frame that was done in-camera.

Try Google Images with 'vertical camera movement blur effect'

To get that bright highlight look try setting the upper layer to Screen.

There's no magic button for this. This was achieved through a combination of techniques. 

• Multiple layers & blending modes, 
• Generative AI, 
• Manual painting/drawing,
• Etc...

If you know who the artist is, maybe they will tell you what's in their secret sauce.  😉

Please post (lores of) the images you want to edit thusly. 

I think the combination of effects involved is a bit much for calling it »one technique« (aside from »collage« as you already did).