Multiple Crashes After 10.5 Pro upgrade

Constant Crashes on Mojave here. 10.5.20 crashes on loading plugins, changing windows or just randomly.
I upgraded from 8.5 that was running like a breeze on these machines, just to get this terrible experience that literally frustrates me to the point that i give up making music.
I ve used Cubase since 1996. Really, I am so bummed by the lack of support on developer side.
On top of everything, I cannot run 8.5 anymore. For whatever reason, I know i could run older versions if I have the licence for the last version - now i cannot even roll back to my stable environment.