Hello as I live not in the USA or russia it seems to be impossible te upgrade my family storage plan. So I am looking for a way to make a daily backup of my iPhones, watches, iPads to a linux computer.

Not possible.

You can manually backup devices to a Windows PC or Mac. But there is no way to create an iCloud server on a Linux machine and have your devices automatically backup to it.

You can change your Apple ID country, to one of the supported countries if you have a payment method for it.

click here ➜ iCloud+ plans and pricing - Apple Support

and click here ➜ Change your Apple ID country or region - Apple Support

As I said, the existing options are either back up directly to a Mac or Windows PC, or change your Apple ID to a country where iCloud Storage is available.

Though looking at the pricing guide in the link above, it does include the Netherlands (Holland) as part of the Euro zone and offers iCloud there.

What exactly happens when you try to upgrade then?

click here ➜ Upgrade to iCloud+ - Apple Support

You can offer feedback to Apple directly by clicking here ➜ Feedback - iCloud - Apple