If you own 2 websites with the same content it doesn't matter what the IP address is, they are still duplicate. Ideally there will be a canonical tag if there is a need for duplicate sites, and possibly hreflang= meta tags if the reason for the duplicate sites is related to regional differences.

Content and ip have no correlation. If the content is duplicate, g (bing and others, too) will know if very quickly.

Is there a corelation between a website IP-adress and the value of a backlink?
Lets say your IP-adress = 123.123.123 (Example IP adresses)

And you have a backlink from 123.123.124, Or even the same 123.123.123 does is have less value than a backlink from 199.999.999?
Is there kind of a relation between those IP-adresses and their value?

I honestly don't know if there's any value to backlinks now, or if Google has just gotten so smart that I can't figure out the value.

Back when I did web design for clients, I always put "web design by blah blah" at the bottom with a link to my site. In the early 2010s that helped a lot, but by 2015 it seemed to have no value. Putting them on different servers had no impact, either.

And then I tried creating a unique page on their site (with their permission, of course) that had a brief paragraph about their website, and linked to my main site twice within the paragraph that fit in with the context (in a non-spammy way). Something like:

This website began in 2005, and was redesigned by <a href='https://www.example.com'>Example</a> in 2009. The new build focused on blah blah and yadda yada. More blah blah blah.

<a href='https://www.example.com/webdesign/'>Example</a> used blah blah and more blah blah when they designed the site...

This didn't seem to have any impact on my SE, either. So after that, I just gave up on trying.

If you own a 2 websites with the same content, how far do you need to change the IP-adress so Google DOENST see it as duplicate?
123.123.124 or does it have to be a complete different IP-adress? And if yes, how much needs to change?

Like the others said, the IP makes no difference at all here. Think of it like this: Google has no idea if the second site is just stealing content from the first, and they definitely don't want to reward a thief! So they try to give all of the value to the original site.

The best thing I can suggest is to use <link rel="canonical" href="https://www.originalsite.com/originalpage/"> on the second site so that Google can find the source easier. The original site will still get the value, but at least the second site won't get punished.

So they try to give all of the value to the original site.

Always assuming they’ve correctly distinguished between original and thief. But that’s a whole nother thread.