Yes, it is sinful.

Proverbs 12.10: "The righteous care for the needs of their animals,
but the kindest acts of the wicked are cruel."

As believers we cannot brush off animal cruelty with nonchalance, let alone with pleasure. The Bible teaches that animals have worth and dignity: Ex. 21-22.14; Dt. 25; Ps. 50.10; even Luke 14.5; as well as Prov. 12.10, that I just quoted. Even the sparrows are under God's compassionate care (Lk. 12.6).

Animal compassion is part of our privileged role as custodians of the world and of the creatures that God made and in which He takes pleasure. C.S. Lewis felt that animal suffering was senseless, and argued that it was precisely because humans are higher than animals in creation's hierarchy that we should oppose animal cruelty. Our very superiority to animals ought to motivate us to prove that we are not ourselves just animals, and we don't enjoy their suffering.

Yes, it is sinful to do this:

Proverbs 17:5: "Whoever mocks the poor shows contempt for their Maker; whoever gloats over disaster will not go unpunished."

1 Corinthians 13:6-7: "Love does not delight in evil but rejoices with the truth. It always protects, always trusts, always hopes, always perseveres."

In Christianity, is it a sin to enjoy the suffering of others if you do not cause or contribute to it, and cannot prevent it even if you wanted to?

For example, there is quite a large number of individuals who enjoy seeing baby animals suffer, particularly monkeys. If a person living nowhere near this suffering, and who has no means to contribute to the welfare of the animals, watches and enjoys videos of this suffering is it sinful? Presume that the uploader of the video either does not profit from the viewcount or is attempting to raise awareness for the welfare of the animal.