If Jesus is God, then why in John 1:18 did he say that “No one has ever seen God; the only God, who is at the Father’s side, he has made him known.”?

The verses in the Bible which teach that no man can see God are in fact referring to no mortal man in this life. Even Moses was refused this honor (Ex. 33:20-23). Mortal man is simply not suited for that exposure. However, what man cannot see in this life, he will see in his immortal life (1 Cor. 13:12; Rev. 22:4). This is known as the beatific (blessed) vision and will be the spiritual climax of the believer to see God face-to-face, to know Him directly in His essence and not merely indirectly as reflected through created things (Rom. 1:18–20).