Shirtless breasts are pg13 safe if there is zero sexual context- ie, an artistic nude. This doesn't look like it has sexual context so it's probably fine there, but I get why you'd be happier leaving it here it's borderline.
We have opt out filters for stuff, so as long as you filter correctly, we're pretty flexible. But yeah- some places have very prude rules so it's good to check ^^; If you are concerned, please feel free to message me and I'll tell you if it's R18 or not