There are basically 4 stages in the production of an image like the 'Galactic Bystanders': Scene setup, linework, colour and adjustments.
For the scene setup, I used ZBrush and my custom comic materials. I rendered the bases of the linework in Keyshot as it allows me to play with the camera settings a bit more. I also kept the ZBrush comic MatCap enabled in Keyshot for the render.

For the linework, I moved the reference render into Procreate and worked on the main features of the illustration. I also refined the line quality and added a bunch of details with the equivalent to a 'ballpoint pen'.

For the colouring, I brought the final linework into Photoshop and use a soft cold palette with simple gradients to set the tone of the image..

After completing the colouring in Photoshop, I added a few photo filters and colour correction layers. To integrate everything, I added a couple of subtle gradients over the whole image and added some textures.

There is also a subtle animation that I did for the NFT and you can watch it on my Foundation or my ArtStation page... hope this helps!