How do you know when to use "absolut" as Modaladverb in German? I just can't find a rule on it. For example, why is it correct to say "absolut richtig" whereas "absolut schön" sounds off?
I don't think this is a question about German language. You have the same problem in any language, but I'll give you an answer anyway:
If something is correct, you very often can proof that it is correct. So, the sentence »this is correct« very often is an objective statement, not influenced by individual meanings.
If you say, something is absolutely correct, you claim that everybody will be firmly convinced in a consensual manner.
But if one person says a red rose is more beautiful than anything else, and another person says, no, the ceiling of the sistine chapel is even more beautiful, and a third person says, no, Lisa Brown, living 3 houses down the road is more beautiful than anything else, you never will get a consensual meaning about this topic. It is not possible to claim an objective statement about beauty.
And so, every statement about beauty will always be subjective, and therefore can't be absolute. This can't be in German, and it can't in any other language.