Dark Souls 3 is developed in a different engine and allows for random people to invade you, and for you to invade or join random people too.

Valheim is more focused on coop, you will not likely be playing with randoms but with friends. While I can't answer if Valheim is completely safe online, it most likely is and as long as you avoid playing with randos (which sucks on Valheim anyways), you'll be safe anywhere.