Lots of people have mentioned rsynx, restic, borgbackup, and others, but which would be best for backing up nextcloud, immich, and radicale? Do all of them have a method of automatically backing up every X days/weeks? Why use one over the other, what are the differences?
The question you’re asking is too broad. Every tool somehow differs from the others, but listing all differences requires in-depth knowledge of each tool and a lot of time.
At the end of the day, every tool somehow backs up your data. CLI interfaces, encryption algorithms, deduplication logic, supported backends, underlying programming languages and a lot more may differ. Identify what’s most important to you, test different solutions and then use the tool that works best for your use-case.