DAVx⁵
CalDAV/CardDAV suite and sync app for Android
...The application integrates with Android's account and synchronization infrastructure, allowing information to appear in compatible calendar, contact, and task applications. DAVx⁵ supports self-hosted services and providers such as Nextcloud, ownCloud, and other standards-compliant servers. It also provides WebDAV file access through Android's Storage Access Framework. Automatic configuration simplifies account setup and resource discovery. Its privacy-focused architecture gives users flexibility in choosing where their personal information is stored and synchronized.