Using older versions of Outlook for Mac for personal email and calendar
Hello Jim,
Thanks for posting into Microsoft Community.
Based on the first error message, we kindly suggest you refer https://support.microsoft.com/en-us/topic/-folder-save-operation-failed-due-to-invalid-property-values-error-message-in-outlook-for-mac-2011-1ec0d3c9-1c0d-539c-2a9c-2cda44e8d1b0 to see whether the issue persists.
About the second error message, if you are Microsoft 365 business subscriber and exchange online account user please try log-in your account in Outlook on the web: https://outlook.office.com/ to check there is any improvement.
Furthermore, please switch to New Outlook for Mac layout to see whether the issue occurs.
Kind Regards,
Tommy