This specific "univ-64bit" build is known for its stability on older hardware running iOS 14. It handles heavy background syncing across different protocols (CalDAV, Exchange, etc.) without the battery drain often seen in poorly optimized calendar apps. In the context of the filename you provided:
Readdle's Calendars is a long-standing premium alternative to the stock iOS Calendar app. It is designed for power users who need to merge tasks and multiple calendar accounts (Google, Outlook, iCloud) into a single, cohesive interface.
The app offers four primary views that outperform the stock Apple Calendar: Granular hourly breakdown.