I assume that you are using NodeJS 12.
The current supported LTS version of NodeJS for the SharePoint Framework is Node.js v8.x and Node.js v10.x (recommended). Node.js v12.x is not currently supported. Notice that Node.js 9.x or 11.x versions are also not supported with SharePoint Framework development.
You need a environment to debug/test your solution, while you could use prod environment to dev/debug SPFx solution, you could dev/debug SPFx solution(webpart) by 'host' workbench /_layouts/15/workbench.aspx without developing the solution to prod.
Using Version Control in VS Code
I needed an account on the tenant domain - It turns out that for SharePoint Online at least you need an account on the domain to access and use the web parts. I am using a persons account who has left the company and I can see the web parts and have no trouble.
As an external user, I could not use the web parts but now I can.