Cannot install addins

I am a Microsoft 365 Personal user. When I try to add the Claude for Excel Addin (for the Desktop version of Excel), I get an error: "Error loading add-ins. One or more add-ins failed to load. See your add-ins.". However, this is not specific to the Claude addin, since every addin gives the same error. When I click on the My-Addins option and then "refresh", I get another error: "Access denied to catalog."

• Signing in and out of Office does not fix the issue.
• Clearing the Office 365 cache did not fix the problem.
• The issue extends to Powerpoint and Word as well. 
• I cannot add any addins to the web versions of Office either.

Interestingly, if I download an XML manifest file, I can use the "Manage my addins" option in the web versions of Office 365 to manually add the addins. But still no luck with the Desktop versions.

Anyone have any thoughts on how to fix this? Do I need to manually reinstall Office 365?

I also noticed that the "Get Add-ins" button in "Account" settings is disabled.