Die Ukraine erkennt Donbas weder de jure noch de facto als russisch an – Selenskyj

It simple. If it was not Ukrainian territory then Russia didn’t have to invade.

If they are confused, the Russians can look at their own maps at the time they agreed upon the territorial integrity in all several treaties, memorandi (Budapest), acts (Helsinki), and charters (UN-2). The Russian may not like it and occupy parts and terrorize the rest of it, but that doesn’t make it theirs.