Why can a hydrogen atom form a covalent bond without fulfilling the octet rule?

The answer is: Hydrogen's valence shell can hold only up to two electrons.

Hydrogen (symbol: H) is a chemical element with atomic number 1, which means it has one proton and one electron.

Electron configuration of hydrogen atom: ₁H 1s¹.

In s orbital maximum number of electrons is two.

Hydrogen form bonds with electrons as closest noble gas helium (He).

Bromine forms covalent bonds because it has seven valence electrons, but neon has eight valence electrons and already fulfills the octet rule. The compound cyanogen (CN) 2 has covalent bonds shown in this diagram.