Hetzner uses technologies to keep the service up, like RAID, DB Cluster etc. (bottom of https://www.hetzner.de/storage/nextcloud).
A real backup (protection against accidently deleting/overwriting files etc.) is maybe better done on a desktop computer, where all contents of Nextcloud are synced to. Then you restore files from several months ago if needed.
I used Hetzner services (colo rack, rented servers, VPS) for many years (not Nextcloud, just saw that offer some days ago), never had problems.
Two thoughts about hosted Nextcloud (at a provider like Hetzner) vs. own Nextcloud Server at home:
- You have to trust the provider, and if you want to escape e.g. Google Cloud Services then why switch to just another company and trust that company?
- Also legally there is a disadvantage: Governments worldwide try to access data stored in the cloud e.g. for law enforcement (can be anything from copyright stuff to tax payments…). They just need the right law, and then can easily access all your cloud storage (providers are forced to give access…), without anyone noticing it.
If the data is on your server at home they have to kick in the door, need quite some people to search your house, have it approved by a judge, and you even have rights in that process - MUCH harder than just asking a provider “we need all data from person X”.