A question

If Donbass doesn’t have a right to self-determination, by which standard does Ukraine have one? How are they allowed to be a state? I thought they were a part of the Russian empire combined with Galicia, named Ukraine in the Soviet Union, where they added Donbass and Crimea to make it a more legitimate-looking “soviet republic”. If they are allowed to be internationally recognized as a state after the constitutional collapse of the Soviet Union, how are Crimea and Donbass not allowed to be internationally recognized as states after the constitutional collapse of Ukraine in 2014?