Does this general hybridization rule really apply?

So this rule is known about hybridization that:
if 4 groups (atoms/pairs of electrons) are attached to the atom -> sp3
if 3 -> sp2
if 2 -> sp


but isn't that true only to specific elements only like carbon/oxygen/nitrogen..?


If you take CCl4, C is sp3, but chlorine has 4 groups around it but it's still not sp3 nor hybridized, it's just an sp3-p bond.


Even for nitrogen like in pyrrole, nirogen has 4 groups around it but it's sp2 because of resonance.


but can someone make it clear? to which elements does that rule apply? what elements undergo hybridization? what elements can they ask about in college regarding that?


Thank you


