This guide is based on personal experience and this post: https://tcg96.github.io/win11geforce9400m.html  

VIdeo on my youtube https://www.youtube.com/watch?v=EfzzJVGw6rw

Key passages:

1 Get Windows 23h2 installed in Legacy Mode (MBR partition scheme) inside the mac. As this family of macs does not allow USB legacy boot, there are two ways to achieve this:
I have burnt the ISO on USB stick with RUFUS in Legacy (or CSM) mode; as you click “START” it will ask you for the TPM baypass hacks that you need. Installed in another computer on the SSD that i moved to the macbook after the initial user setup was completed.

A user  called @rozgray on the original post video comments section wrote this alternate solution that i did not test:

“you can also achieve a legacy install by manually installing windows with dism, and configuring bootloader and bootsector from the command prompt within the windows installer (even when booted in uefi mode!), which removes the annoying requirement for a disc: just make a normal windows install usb (i use windiskwriter in a different macos mac) boot from it and open command prompt clean the disk and make sure its mbr, all through diskpart apply the image with dism make the boot files with bcdedit and at last, the most important part is to set the mbr boot sector with bootsec, so it can actually boot then just take out the thumb drive, restart, and windows should be installed in legacy mode”

2 Install the bootcamp drivers; i used Brigadier to download them and removed the nVidia Driver folder before launching the installer, as i manually downloaded the latest 342.01 .
Before reboot i went to\Windows\System32\Drivers and replaced MacHALDriver.sys with this newer version , if you don’t do this the system will be bricked.

This is required to get the tray icon that enables brightness control for display and keyboard.

Another option worth testing is this bettercamp_w11

3 Download Throttlestop and start setting up for best performance and efficiency. As this family of CPU has no offset but only fixed voltage, i might aswell set the CPU to 100% all the time in Windows energy preferences (you can still use the balanced power plan) and set the Processor performance time check interval to the max value of 5000 using Power Settings Explorer . I started to set the multiplier at the max value (10.5 for my cpu) and then reduce the voltage until windows crashed, then started to test using Geekbench6 using slightly higher value. My P8800 cpu would crash in desktop at a very nice round 1.000v and ended up being perfectly stable at 1.0250 after multiple Geekbench 6 runs; this also proved stable during the whole process afterwards and different web benchmarks that i was running to keep track of performance improvements between steps.

4 Update touchpad driver with the ones on this github https://github.com/vitoplantamura/MagicTrackpad2ForWindows

5 Ran both ChrisTitus and Raphire debloat scripts. Windows RAM usage at boot dropped from 2 to 1,4gb. Benchmarks scores rised slightly.
While testing memory usage, i noticed that the system actually had 2x4gb installed, but one bank only showed up once in maybe 10 reboots. I determined that the slot closer to the keyboard was not working (even after contact cleaner) so i swapped the 1066 mem with a single 4gb 1333. These machines are not usually stable with two 1333 installed, but a single one worked fine. This improved benchmark scores slightly.

6 Used InSpectre to disable Meltdown patches, improved benchmark scores across the board. Added Program Files X86 & Programs Files in the Windows Defender Exclusion list.

7 Set some windows CPU timers to their max value – notably “Processor performance time check interval” using WindowsPowerSettingsExplorer . Very minor improvement in geekbench multi, better than nothing.

8 ran AtlasOs 0.4 script, keeping Windows Defender on. Very minor impact if any, as i already ran a lot of scripts before. Ram usage a boot is between 1,3 and 1,4gb. Disabling Defender would be a HUGE improvement in general responsiveness but the machine need to be used by a normal person.

I disabled the BootCamp try icon to run the last round of tests, on the right i also noted the initial result before any tuning. Keep in mind the initial scores were taken with 1066 ram.

SilverBench around 4690 – before 4150

Speedometer3.1  around 5,2 before 4,4

SpeedPower.run around 86 – before 74

WebXPRT always 22 – before 21 (smallest improvement)

Geekbench 6 around 343 single – 560 multi – before 310 – 480

133 CPU and 10,06fps on Cinebench r15 – 101 and 8,2 before everything, after undervolt it was 124 already; i can get it to 135 with high priority on cold boot

710 CPU on Cinebench R23, topping at 88C