Using the kernel parameter memmap with grub2 boot loader causes kernel hang during boot. The systems freezes directly after issuing
Loading initial ramdisk ...
The root cause is that the "$" character needs to be escaped even in /boot/grub2/grub.cfg.
Multiple escaping is necessary when using the "official" configuratino files due to several bash sourcing and $-sign "interpretations".
This is documented e.g. in
* memmap option causes inexplicable hang -

This error is very hard to detect and I spend "a lot of time" chasing a non existent graphics issue (KVM, nomodeset, etc).
Eventually, trying to install a fresh OS12.3 (this bug applies here too!) and fiddling with a very specific "vga=0x0361" setting, the screen switched mode and displayed
PANIC: early exception 08 rip 246:10 error 8158c98c cr2 0
This error message does not appear "usually"!
Chasing this error message (e.g. [SOLVED] PANIC: early exception 08 rip 246:10 after upgrading from 2 to 4GB RAM) I finally tracked it down to the "$-escaping" issue.

To do:
(Multiply) Escape the $-sign in all grub2 configuration files acc.
* memmap option causes inexplicable hang -

Additional info:
I reported this bug