The other comment, from sib, already shows that there is an example I'd missed of a climate protest leading to a piece of art getting damaged - albeit in a mino

The other comment, from sib, already shows that there is an example I'd missed of a climate protest leading to a piece of art getting damaged - albeit in a minor way (and I think sounds like it was accidental too, that they were again aiming to damage the case not the painting itself - otherwise they would have done more than light scratching / would've picked a painting without that type of strong case). But your link isn't about climate protestors at all, and it's barely even about art - the painting those people targeted wasn't picked for being a well known and well liked picture, but because of the politics 100 years ago of the person in the painting. Quite a different situation, and entirely different reason for protest.