Hybrid Vigour is a desirable consequence of breeding different types of domestic livestock (cows, chickens, etc), which makes larger and healthier animals. And as far as I know doesn’t render them infertile.

And it is well known “mixed” dogs, or “mutts”, are healthier than their purebred counterparts, and they can obviously still have puppies.

Slightly less well known would be that humans and Neanderthals interbred, to the point that every person on earth right now has some Neanderthal DNA.

grizzly bears and polar bears are the same species, but different sub-species. Same for humans and Neanderthals, or a German shepperd and a black lab.

Other hybrids, like a lion and a tiger, or a horse and a donkey, are different species, and their offspring (a liger or a tigon) are infertile.

One question that may arise is “how do you differentiate a species from a sub species?”. Well conveniently enough, a common definition (although not universally accepted) is based on this exact question: if two animals can produce fertile offspring, they are classified as different subspecies. If not, then they are different species.

Note: not a biologist, this is my armchair understanding. Likely missing a lot of nuance.