Despite this, it was Eru who brought Gandalf back and set him on the path to defeating Sauron, making Gandalf one of the very few people to not only return from death but also interact with the lord of all creation.

Source: https://www.cbr.com/gandalf-resurrection-explained-lord-of-rings/

When the Númenóreans broke the Ban of the Valar — the deities forbade the Men of Númenor from sailing too far west from the island — Eru Ilúvatar, the Creator and supreme deity of Arda, punished them by drowning the island.

Source: https://gamerant.com/lotr-what-caused-downfall-of-gondor/