Report possibility for responses on an event.

As far as I investigated, it’s not possible to generate a report to check and/or visualise the responses on the invitations of an event.
Not in the module and not by a report.

Could be handy (if not essential)

Yes, the Events module is kind of a “special module” in SuiteCRM, some things about it are programmed differently, and it is less completely integrated into the generic SuiteCRM features (like reports).

I would consider getting the report from SQL in phpMyAdmin, it shouldn’t be too difficult to produce a CSV that you can then make pretty in Excel.