I've been looking into options for how we deal with Calendars on SharePoint. During the process, I found this option of viewing a Calendar App or Events List in the modern environment (sharepoint online - Migrate Classic Calendar to Modern - SharePoint Stack Exchange). I've applied this to convert a classic list on SharePoint and ran into an oddity. I added two Events to one of our sites, one was an all-day event for Halloween, and the other was for a Trunk or Treat going from 4:30 PM PDT to 7:00 PM PDT the same day. When viewed through ../Events/calendar.aspx in the classic view the times show correctly — all day on the 31st and 4:30 PM to 7:00 PM respectively. When viewed through ../Events/ModernCalendar.aspx the all-day event shows the UTC equivalent of 12:00 AM to 11:59 PM on October 31 — 5:00 PM October 30 through 4:59 PM October 31, and the Trunk or Treat still shows as 4:30 PM PDT to 7:00 PM PDT on October 31.