When creating a Flow to sync events between two calendars in O365, there is no dynamic content that allows for attachments to carry over from the orginal event to the created event on the secondary calendar. As well, there is no option for this when the event is updated. I would like to see these options available. Below is a response from Microsoft Support stating the exact issue.
I verified the scenario of meetings with attachments and it does not seem to be possible to create event in the 2nd calendar with attachment.
The reason is that when an event is created, the connector fetches certain metadata from Office. This metadata includes event related details but not attachment details and therefore, we wont be able to replicate this at the 2nd calendar.
This is more by design scenario as of now. You can share or vote for ideas at our forum: