I know I'm being a bit dense here........

[Howard_F]

....but how do I create something like this?

[Monika Gause]

Those are isometric drawings.

So you dirst build them flat: a black and a white square with rounded corners and then use isometric transformatione methods to make them into the distortion. Then duplicate the white aquare and move in a certain angle. Then draw lines that connect the front and back with lines. Then use the shapebuilder tool.

There are scripts, plugins and actions to make the isometric transformations. You can search on the web for isometric tutorials.

[Howard_F]

Thank you Monika, I understand all that, but in this YT https://youtu.be/cvgFjU9CJnQ?t=359 he (or she, or they or them) have created a Style which can be applied to other objects. Have I missed something?

[Monika Gause · Accepted solution]

If you want to know how that person did it, just ask them.

Here's how I would do it with effects: https://youtu.be/LcvR5IwzVss 

[Howard_F]

Thank you Monika, I did ask them and it's the next tutorial. Thanks for your post and reference.

[Howard_F]

Perfect. thank you Monika. Nice portfolio btw on Behance.

[Howard_F]

Monika. Not sure why I am getting these glitches. Any ideas?

[Monika Gause]

If that doesn't go away in CPU preview, then:

Can you perhaps share the file?

Just rename it to PDF, then you can upload it in the forum

[Howard_F]

Thank you Monika. Attached.

[Monika Gause · Accepted solution]

Those are issues with the precision of the 3D effect.

The one on the stroke will be gone, when you change the stroke corners to rounded in the stroke panel for the stroke on the layer.

The issue with the corner will be gone when you adjust the settings in the effect. I tried the length of the extrusion. It comes and goes - just set it to a value where it's gone.