Hi Endre, to answer your many questions;

Take your time, read the entire thing first before doing anything.

First on i followed the link to the patch file: https://bugzilla.kernel.org/attachment.cgi?id=305236&action=diff

I downloaded the file by pressing 'view' button on that website.

second I went to the kernel.org documentation to find the following page: https://www.kernel.org/doc/html/v4.14/process/applying-patches.html

it explains how to patch a kernel

the required packages are (already in the apt command line :p) found here:https://people.montefiore.uliege.be/gain/courses/info0940/tutorials/tutorial3/compilekernel.html

sudo apt install build-essential libncurses5-dev libssl-dev flex libelf-dev bc bison gcc make bc dwarves libelf-dev

After this you should have: the patch file and all the packages required for patching, i personally used debian, but it's perfectly doable on ubuntu i guess.

then head over to kernel.org and download a kernel. i suggest as close as possible to the current kernel your os is running.
I personally downloaded 6.1.59, and will today try with another kernel to see if results are persistent.
i will test it on kernel 5.15.136.

decompress the downloaded kernel.
from here on all commands are issued as the root user.
aquire root privileges. (sudo su)
enter the decompressed kernel root directory so you are in linux-image-X/
then as root in that directory run patch -p1 < /path/to/downloaded_patch

let is complete
it should notify you when completed.
make menuconfig and just immediatly press save and follow default prompt.
then exit.


next up is to build the actual kernel itself, depending on the hard disk speed it could take 3 hours. my laptop (the ryzen 5-7520u combined with a usb ssd took about 3 and a half hours) you will need about 60Gb of hard disk/ssd space. 
(today i will run it in my ramdisk as my desktop workstation has 64Gb of ram for ramdisk purposes :p) i will post total build time after it's done.

build the kernel by running: make
 seems simple enough, just type make and press enter, now get a coffee or a tea or go watch grass grow 
 because now it will start building, it will take time.

if you are running ubuntu:
 make might complain about certificates (No rule to make target 'debian/canonical-certs.pem) , nothing 
 too bad, !!just run the following!!

scripts/config --disable SYSTEM_TRUSTED_KEYS
scripts/config --disable SYSTEM_REVOCATION_KEYS


 and then run make again.
 if it asks something just press enter.


 then let it cook until al dente;


 then you will need to make the modules for the kernel i don't exactly know what this does but it's 
 important.

run: sudo make modules
 this shouldn't take too long to complete.
 After this is done:
 congrats, you now have a patched kernel, but what to do with it now?

installing it in the current running system assuming all apt packages from compiling are present :
 make install

after a reboot into the installed kernel (grub should do this automatically as the version is later than the currently installed ones don't quote me on this :p) the keyboard/touchpad should be working now. if not then maybe a step failed.

what if i need to reinstall my distro?
 well, back the patched kernel up, preferably compressed, to a flash drive or whatever.
 install the new distro using external kb and mouse and then copy over the patched kernel, it can be 
 installed by decompressing it, and running the following 3 commands in it's root directory:
 #cd linux-image-XX < x is the version :-) do not forget to manually cd

 sudo apt-get install build-essential libncurses-dev bison flex libssl-dev libelf-dev
 sudo make modules_install
 sudo make install

if it complains about needing to run make before make install, prepare for another 3 hours. perhaps run make -j 4 (j 4 will run make over 4 job making it theoretically 4 times faster.)

this will conclude the patch.
make sure after rebooting that you freeze the kernel package in apt.
list the packages by running
sudo apt list --installed | grep linux-image
then take note of the currently installed kernel, and take the one without much other text for example in my case it was:
sudo apt-mark linux-image-amd64/stable


and that's it.
I hope this works for you too;
Happy patching!

edit;
i started compiling the 5.15.136 kernel on my workstation, i added a few extra lines in the manual above.
if you run into something, google will have the answer ready since it will mostly be dependencies and packages.
I'm now testing the kernel patch on zorin os 16.3 too which is based on ubuhtu 20.04.2
I will report my findings here.

edit edit;

been compiling the kernels (5.15.136) in zorin os 16.3 (ubuntu 20.04.2), been having issues with the make install, turns out you need to disable CONFIG_X86_X32 in the .config file of the kernel after running make menuconfig. i might restrructure this post after i'm done expermimenting, tomorrow i have an entire day to experiment with it.

edit edit edit;

I only got 6.1.59 working on debian, zorin os was a bust so i suggest you switch it up to use debian until an official fix is here.
I'm done trying for today... going to touch some grass now.