Using New Outlook on Windows for personal email, calendar, and contact management
I completely understand your frustration. Having to switch between new Outlook and classic Outlook because each version breaks a different part of your workflow is not a reasonable experience, especially when you rely on Google Calendar integration and rules every day.
Microsoft is gradually moving toward new Outlook, but classic Outlook has not been discontinued and is expected to remain available until at least 2029. Microsoft also acknowledges that feature parity is incomplete and currently recommends running both versions side by side when required features are not yet available in new Outlook.
For the rules issue, could you clarify whether the rules are being applied to a Gmail account or a Microsoft/Exchange account, and what the rule is supposed to do? That distinction may help determine whether this is a current limitation or a specific malfunction.