https://www.bbc.com/news/entertainment-arts-63254878
First thing, it wasn't damaged. However, although the BBC article is correct in other respects, the National Gallery does not put glass over its paintings, it had a protective layer of clear acrylic varnish so the varnish could be washed off without damaging the oil. It appears the varnish did its job and did not need to be removed or replaced.
The second thing, most people don't know that there are five surviving Van Gogh sunflowers. The four on public display are actually early studies for the fifth, which was renowned for decades as the most expensive painting ever. I was graced to see it in the 1960s before it vanished into its private collection, and it was incredible--the palette strokes were inches thick, making it three-dimensional. Most people assume Van Gogh painted it only once and have heard about its huge value so they assume, as the protestors probably did, that it was the attacked painting. That is to say, it is a rare painting but not irreplaceable, in fact, Van Gogh already replaced it with a much better version himself. Even so, it is definitely still rare, and it's rather a shame all five surviving sunflowers will never be viewed together, at least in our lifetimes.