In Cubase 12, We can’t find “LoopMash” in VSTi Instrument selector now.
I found resolving it in a Japanese web-page.(see under of the middle the page)
If you couldn’t translate in English, give reply this topic then I’ll post it.
See this thread: Can't find Prologue / Mystic / Spector in Cubase 12
It worked for me.
Thunk you! PulsePsycle 