Black screen after rebooting from within ZorinOS

With pro license you can get help directly from zorin team:

Where is grub installed - on which drive? Is it installed together with Windows boatloader in EFI partition or separately?

As the kernel 6.16 is a really new one, try it also with 6.12 or 6.14 and use cappelican or tuxinvader mainline tool: