Hi all!
I had to put this problem off for a while to focus on some more urgent stuff, but eventually, it looks like I got rid of all the issues I was experiencing Here is what worked for me - maybe it will help some other people too:



(1) restoring Windows entry on GRUB screen


I needed to add in /etc/default/grub the following line and only after this upgrading GRUB worked as expected:

GRUB_DISABLE_OS_PROBER=false

The line was completely missing from my configuration file, but some people have it and it's just commented out in their grub files. This line enabled OS-Prober which detected Windows and added it to my GRUB screen.
If anyone faces the same issue as I did, do remember to make a backup of your grub configuration before editing it:
cp /etc/default/grub ~/grub
And after adding the OS-Prober line, update your GRUB with:
sudo update-grub
This command will probably output something like 'Found Windows Boot Manager (...) Adding boot menu entry for UEFI Firmware Settings'. And after restarting your computer, you should see the missing Windows Bootloader entry back on your GRUB screen.



(2) fixing broken UEFI


To regain access to my UEFI, I decided to reset its battery using the pinehole reset button on the bottom part of my laptop chase. In the case of my computer, it has a battery symbol next to it and one should be pressing this button for ~30 seconds with a paper clip or something like this, and then leave the computer turned off for a while.
My computer still launched GRUB the first time I turned it on after this operation. I then started Windows and installed every available update there. It began booting directly into Windows and skipping GRUB after that, but I could access UEFI again. My UEFI actually got upgraded as a result of these steps. I checked its version before and after resetting the computer (here are a few Windows cmd commands to check BIOS version: wmic bios get smbiosbiosversion ; systeminfo | findstr /i bios ; powershell Get-WmiObject win32_bios). And finally, I restored GRUB Bootloader by changing the boot priority order in UEFI, in its Boot tab. I simply set GRUB to be at the top of the list and saved the change. I also made sure that Secure Boot was disabled (making this change required first setting a temporary supervisor password for my BIOS). And the next time I restarted my computer, it happily launched GRUB rather than Windows Bootloader.



(3) ACPI BIOS Error


I did the things above and then I also updated Kali. My kernel got upgraded to version 6.0, and the ACPI BIOS Error was already gone at this stage. I'm not sure if it was upgrading BIOS, upgrading my Linux kernel or something else that fixed this. Maybe the next person having the same issue will be able to examine it in more detail for us