Just last week I “fixed’ two 2011 MacBook Pro 15” by disabling the AMD graphics in firmware and deleting kexts, as I assume you’ve done. Parallels and Paratext confined to work fine.
I’ll assume you’ve reinstalled the Parallels drivers in the VM and played around with the video memory allocation in the VM settings.
Blessings,
LivingField
This message was sent from my phone. please forgive abbreviated grammar, lack of politeness, and wrong spellings.