Reset your workspace logo

The default logo for Atlas workspaces is generated by Microsoft 365 using the name of the workspace as the letters on a coloured background, for example:

If you have sufficient permissions on the workspace you can change this to a custom logo using the Change the look link under the SharePoint Settings menu, but if you want to remove the custom logo and go back to using the default configuration you will find that this cannot be done - instead you are simply forced to upload a new logo.

However, there is a way to reset the workspace logo from a "classic" screen that is completely hidden from the UI in Knowledge workspaces, and although it is available in Communications workspaces it is buried in the Site settings screen.

Go to the homepage of the workspace whose logo you want to reset
In the Browser Address bar look at your workspace URL and add the following:
/_layouts/15/prjsetng.aspx
So if your workspace was at https://tenantname.sharepoint.com/sites/atlas you would want to update the url to https://tenantname.sharepoint.com/sites/atlas/_layouts/15/prjsetng.aspx
Press enter to navigate to that page. This is a "classic" settings page but it can still be used to change or reset the logo. You will see the a screen like this showing your current logo:
To reset the logo, delete all text from the box indicated in the screenshot above, then click the OK button in the bottom right:
You will see the logo replaced with the "classic" default logo in classic screens...
...but if you click the logo to go back to the workspace homepage you will see it has been reset to the Modern default of letters on a coloured background.