Dear @denk,
Thank you for reaching out Q&A Forum!
We understand that you're having trouble with Excel Online, when you are unable to use the "Save a Copy" feature and change the save file location.
Based on our research, Microsoft 365 for the web is designed to let you view and edit documents stored in OneDrive directly from your browser. Microsoft 365 for the web gives you the full functionality of editing without having to start up an Office program. So that, you cannot change the saving location on Excel Online because it connects direct to OneDrive.
Link for your reference: Using Office for the web in OneDrive - Microsoft Support
Work with worksheet data in OneDrive - Microsoft Support
As we reviewed in our Excel Online, there is no 'Save a Copy' option available in this version.
The 'Save a Copy' option is available in the Microsoft 365 Excel app. With this option, you can choose the location where you want to save the file in File Explorer.
Since Dropbox is a third-party service, there may be occasional compatibility issues or conflicts when used alongside Microsoft tools. For a smoother and more reliable experience, we recommend considering OneDrive. As a Microsoft product, OneDrive offers stronger compatibility with the Microsoft ecosystem.
If there’s any misunderstanding from our side, please don’t hesitate to let us know so we can better assist you.
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