Same here. Just upgraded to 10.5 from 10.0 on Mojave, and it’s almost COMPLETELY unusable, even with just two audio tracks and one VST plugin. 90% of the time I get that spinning coloured pinwheel that every Mac user just loves to see… can’t stop/play the session, open the mixer, or even quit the program without clicking the mouse 1,000,000 times to get Cubase to respond.
SO GLAD I spent my money to “upgrade” to an unusable pile of garbage!