Thanks for the continued help on this subject.

I did a 'Microsoft Store' uninstall, as the type of previous install was one with a version and build number. So the uninstall took place via Control Panel and the 'Programs and Features' option.

Once completed I restarted my laptop then installed my subscription copy of Microsoft 365 Personal.

When opening a blank Excel workbook it does so in Read Only mode. There is a banner warning message again stating 'SIGN IN TO SAVE'.
There is also, for reference, the 'Sign In' and 'Buy Microsoft 365' buttons displaying in the top right corner of the screen in the task bar.
When I sign into my hotmail account, I am just returned to the blank workbook as above.

If I attempt to open an old Excel file I have in my downloads, the previously mentioned 'Enable Editing' warning message is displayed and it then asks me to Save to OneDrive.
As per the blank workbook issue, when I sign into my hotmail account, I'm simply returned to the file with the enable editing warning message.

So clearly something not clicking into place with the install.
Am I missing a step? Once the install is downloaded and installed, should I be accessing my Microsoft 365 Personal account and activating it somehow before just opening up Excel?

Ben.