Amazon maintains a page with all current generation EC2 instance types. Data was generally extracted from this page. However, there were some details that have come from family specific pages (e.g. i3en family) or new instance type blog announcements (e.g. c6g).
All data was pulled from Google's Compute Engine machine types page. While it appears that Google has far less types and options, Google allows for greater flexibility and decisions to be made by the user. Users can more easily add GPUs or select specific processor types when launching instances.
Microsoft has individual pages for every Azure virtual machine size. Data was pulled from each size's page. Additionally, Azure explains the naming conventions used to denote features and specifications.