Ability to show declined events
When the response for a calendar item is set to Declined in Microsoft Office 365, the item disappears completely from both the Microsoft Office 365 and the Evolution calendars. It would be more useful to allow the record to persist with a user interface element that denotes the response status. Using strike-though text for the entry is a good way to indicate declined status. This would allow a user to maintain awareness that a meeting is still being held, even if they are not planning to attend.
For reference, Microsoft Support publishes an article that may be relevant: https://support.office.com/en-us/article/Show-a-declined-meeting-on-my-calendar-24E81B9B-3906-4C02-8B63-F97B02161763. In the case of Microsoft's Outlook product "There is no way to show a declined meeting on your calendar." However, it is unclear if this is due to a poor design decision in their user interface or poor handling of the data on the back-end. If the data is still available from the server, then perhaps Evolution has an opportunity to display the declined item.
Test System: evolution-3.28.5-2.el7.x86_64, evolution-ews-3.28.5-1.el7.x86_64, evolution-data-server-langpacks-3.28.5-1.el7.noarch, evolution-langpacks-3.28.5-2.el7.noarch, evolution-ews-langpacks-3.28.5-1.el7.noarch, evolution-data-server-3.28.5-1.el7.x86_64, CentOS Linux release 7.6.1810 (Core), Account type GOA:ews.