I've been using Nextcloud (and before that, ownCloud), an open source alternative to file syncing and storage services like Dropbox and Google Drive, for many years. It's been both reliable and useful, and it respects my privacy.
While Nextcloud is great at both syncing and storage, it's much more than a place to dump your files. Thanks to applications that you can fold into Nextcloud, it becomes more of an information hub than a storage space.
While I usually interact with Nextcloud using the desktop client or in a browser, I'm not always at my computer (or any computer that I trust). So it's important that I can work with Nextcloud using my LineageOS-powered (or Android) smartphone or tablet.