GNOME Calendar has gotten *so good*, it just handles ICS files, multi-day events, multiple calendars, and mismatched timezones so well now. Hands down my favorite calendar app on any platform. If there's a "most improved app award", surely it must be a contender.
@nathandyer what I find great with GNOME Calendar is I can sync it effortlessly with my Nextcloud Calendar on my PCs. On my Android phone I need an app for synchronization (DAVx⁵).