What is the normal process to create mockups like this? Are they created in 3D and then in photoshop?
Would be a great help if you guys can help me.
If you have 'real' objects to include in your images, you would be much better off using proper 3D software, as Photoshop is not designed for 3D. Blender is a completely free open-source project that has been developed for many years, is highly stable, runs on any platform, and is a viable alternative to $x000 applications like Maya. Once you start to use Blender, you will never even consider Photoshop again when you hear the word '3D'. Check out Blender.org
You can start by creating a small lightbox with white nylon, a simple blank sheet, a adjustable light, a tripod along with a smart phone or professional DSLR camera. There are plenty of DIY videos available how to do that. Take a look here: How to make a mini photo studio. Of course creating your own little studio requires some extra work. You’ll find affordable photo studio kit solutions for under $50 on eBay.
There is no doubt that such mockups are created using dedicated 3D Software, I had personally started Blender to make my own style of mockups to further use on the Photoshop since the Blender is open-source and very light program to explore possibilities for 3D illustration.