Microsoft has provided a solution for this bug, you need to add this registry value [HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Options] and set its value to
"BrowserEmulationModeConfig"=dword:00000003
To apply this solution, follow the steps below:
If you do not want to apply this fix you need to contact your IT department to downgrade your version to a version that side panel was working with.
As a workaround, downgrading to an earlier version will address the issue.
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