Sound and power consumption. At least in my case those are important if I was going to store data at my mothers house. Power consumption might not matter that much, but HDD sound definetly does. And even with spinning rust hardware cost would be somewhere around 250€ compared to ~20€/month of cloud storage.

YMMV, in my scenario it’s just easier to use a cloud provider.

That absolutely works, but when I built my offsite backup to hetzner I also thought about setting up own hardware and came to conclusion that for myself it doesn’t really make a ton of sense. New RPi + 4TB ssd/m.2 drive with accessories adds up to something around 400€ (if that’s even enough today), or few years worth of cloud backups. With own hardware there’s always need to maintain it and hardware failures are always an option, so for me it makes more sense to just rely on big players with offsite backups. Your case might be different for various reasons, but sometimes renting capacity just makes more sense in the big picture.

I’m using proxmox backup server to make copies of full virtual machines, it takes care of encryption and verification of the data, so it’s not exactly the same than your scenario. Borg Backup is commonly recommended, but restic and dejadup are worth checking out too.

I use hetzner storagebox for similar needs. It’s not encrypted, so you need to manage that by yourself, but they support a ton of protocols and pricing is decent, even if they’re increasing the price shortly.