A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi Adam,
It is not feasible to change the version of documents from default numeric to alpha in SharePoint online. Version numbers in SharePoint online are automatically added each time you create a new version. In a list or library that has major versioning enabled, the versions have whole numbers. For more information, How does versioning work in a list or library?
I would suggest you submit your feedback to our User Voice. Your providing feedback is the best way to perfect our products and services.
Thanks for your understanding.
Yoga