An account's refresh action now works for iCloud, Fastmail and other CalDAV accounts. It rechecks the server for calendars added or deleted since you connected, the same way it already did for Google and Outlook.
Connecting a CalDAV calendar that another of your accounts already holds now says it is already connected, instead of importing a second copy of the same calendar.
Keeper.sh also stops sending copies to a Google calendar your account can only read, such as a shared calendar where you were not given permission to make changes. Before this release, it kept retrying those calendars on every sync. A destination calendar that times out is now retried less often until it responds, so it does not hold up your other calendars.
Event times also resolve the same way everywhere Keeper.sh reads or writes them: CalDAV calendars, calendar links, repeating events, Outlook copies, all-day events and the free-time answers given to assistants.
Linked accounts and calendars explains what you can do with each calendar on an account.