As many as four electrons can occupy the same orbital. Is this always true, sometimes true or never true.
In the electronic configuration of atoms, each electron can be uniquely identified by 4 quantum numbers. These are the primary quantum number n, the azimuthal quantum number l, the magnetic quantum number `m_l` and the spin quantum number `m_s` . Atomic orbitals are defined by the first 3 quantum numbers. Each atomic orbital can have two electrons with opposite spin, denoted as +1/2 and -1/2. It is not possible to have more than two electrons in the same orbital as that would give the same four quantum numbers to more than one electron in an atom which is not allowed by the Pauli exclusion principle.
It is never true that as many as four electrons occupy the same orbital.