We can only speak of entropy change, $dS$, when I mention Clausius as $$dS=δQ/T$$
However, according to Boltzmann, entropy is defined as $S=K\ln\Omega$
My question is, is the $S$ according to Boltzmann an entropy change as well? Or is it the entropy of the state whose disorder number is $\Omega$ and accordingly, $ds=k\ln(\Omega_2/\Omega_1)$?
My question is, is the 𝑆 according to Boltzmann an entropy change as well?
No -- Boltzmann gives a value to the entropy, not just the change in entropy.
Even in pure thermodynamics, (i.e., using Clausius's definition), the third law of thermodynamics also fixes the absolute value of the entropy. The third law says that the entropy must approach a constant at zero temperature, where the constant is given by Boltzmann's constant times the natural log of the number of degenerate ground states of the system.
