Das ist aber ein schöner Name

I have just seen this sentence which means “That is such a nice name”.
In which situations does “aber” also means “such”? I only thought it could be used to express “but”.
 

I think aber is a modal particle in this sentence.
Modal particles express the mood or attitude to what is being said and have no direct translation in English.
You can google "German modal particles" for explanations.
This is German with Jenny's version:
https://www.youtube.com/watch?v=2se5NPY94FQ

The modal particle aber can be used to express positive or negative surprise.

It is an advanced subject, Jenny rates it as C1/C2, but it is useful to be able to recognise them as otherwise they can be confusing.  I had a lot of trouble with them until I discovered what they were.
Apparently the next version of Rocket German will have something on them.