Hi @Anonymous ,
Could you please share a bit more about the data structure of "_selectedCalendarEvent" variable?
Based on the issue that you mentioned, I have made a test on my side, and don't have the issue that you mentioned. The data structure of my _selectedCalendarEvent variable as below:


The _selectedCalendarEvent.RequiredAttendees formula would return the following email address:

If you want to get the corresponding display name based on each email address, please take a try with the following formula:

ForAll(
Filter(Split(_selectedCalendarEvent.RequiredAttendees, ";"), !IsBlank(Result)),
Office365Users.UserProfileV2(Result).displayName
)
Note: You need to add the Office365Users connection in your app firstly
You could consider add a Data Table in your app, set the Items property to above ForAll formula. Then enable the Value field within the Data Table, then display name list would be listed:

On your side, please make sure the _selectedCalendarEvent.RequiredAttendees formula returns a string value rather than a table value or record value. Also please make sure you specify proper Office365Users.UserProfileV2() function within the ForAll function.
Best regards,