Using Classic Outlook on Windows for personal email, calendar, and contact management
Since the new Report button is the long-term solution for M365 it would be best to keep it. The platforms it supports are documented here, Report phishing and suspicious emails in Outlook for admins - Microsoft Defender for Office 365 | Microsoft Learn.
If the Report button addresses your needs, you can remove the Report Message and Report Phishing add-ins from the Admin Portal, Deploy add-ins in the admin center - Microsoft 365 admin | Microsoft Learn. You can test making the change on one or a couple users and make sure everything works the way you expect before removing those for everyone.