Love heart notification

Sadly the "heart" shape is one of the more common ones used by apps of different types, and there are literally millions of apps so an immense number that use heart icons. And that's a particularly generic one, with no real distinguishing features, so it's not very likely anyone will be able to give a definite answer.

I know it's not the answer you want, but your best bet is probably to ask the person who sent you the screenshot.

(Incidentally the colour isn't distinctive either: all notification icons are supposed to be monochrome these days, and it's only black because you have a light theme - on my phone it would be white).