Automatically generate product variations
Well, I did have a look around I could not get Commerce Bulk module to install. 
Then I saw https://www.drupal.org/project/commerce/issues/2755529, which will be a sweet feature when it has been merged. I could not get the patch to apply so I ended up creating a sandbox module based on this and here we go:
https://www.drupal.org/sandbox/taggartj/3104497

Judging by your rank you will know how to get the code. 

https://git.drupalcode.org/sandbox/taggartj-3104497/commit/7997ee4

This module will give you a route (no link yet):

You need to create at least one Product variation manually, then go to: 

"/product/PRODUCTID/variations/VARIATIONID/bulk-generate"

or example /product/331/variations/1/bulk-generate, for it to allow you to bulk generate your variations.