With the decay and destruction of everything in Zimbabwe it is/must be reasonable to assume that the CAA Authority is also by now dysfunctional and cannot responsibly cary out its regulatory and oversight responsibilities.
Need also not be a wizzard to hazard a guess that the ZCAA is staffed by Mugabe cronies, like everywhere and things iin Zimbabwe, because after all its a small cash cow for the government.
This, together with the rumours of an official partnership (of convenience) between Avient and senior officers of the Zimbabwe National Defence Force, should be more than sufficient reason for the EU to seriously look at the morality and desirability of allowing the aircraft in question, and any Zimbawean registrations for that matter, into European airspace.
Avient's past acknowledgement of their support to and association with this evil regime should just make matters worse and compound the issue.
If Mozambique, Swaziland, DRC etc etc are banned by the EU, there are ample reasons by now to also ban the Zimbabwe register.