Hmm, as a datapoint, I just tried creating an Outlook event via the automation for 28 Feb and it worked as expected, here's the date field set to display as European
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And the created event is in +8 as that's my timezone, and this is the automation result:
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And here's the date listed in the email invite:
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I also tried changing the display of the field to be US to see if that changed anything and that worked fine:
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If I were you I'd try creating a new automation to create an Outlook event with a new Date field and see if that works. If it does, then we rule out the Base being an issue. You could then update the new automation to use the original Date field to see if that works, etc and proceed to rule stuff out that way?