( ) Chinese invented lots of everyday things, like ink

The gallery bought( )Monet recently for €20 million!

What should be articles in () and why

Sehen Sie eine Übersetzung

The Chinese invented lots of everyday things, like ink.
We say "the" here because we are talking about all Chinese people together, not just one Chinese person.

The gallery bought a Monet (painting) recently for 20 million euros.
We say "a" here because we are talking about one specific painting, which we have not mentioned before.

If you have talked about it before the listener knows which one you mean and you say "the".

Example:
Many Monet paintings have been on sale this month. My gallery bought a Monet called "Garden of Roses". It is beautiful and everyone likes it. The Monet is now the best painting in our collection.

(The first time we talk about that painting we say "a". Once we know which Monet painting we are talking about we say "the".)