B450 Tomahawk, I... don't recall a heatsink ? Checking the box after this postWhat motherboard do you have? It'd be REALLY rare for it to come without a heatsink on the M2 slots.
A quick look at a TomsHardware review confirms that the drive will work with PCIe 3 but will be slower, obviously and yes the drive does run hot so you'd need a heatsink on it.
Not against buying one anyway, it's not pricey IIRC.