This is not important, but if you intend to use some SNAP application right now, before you reboot, then you will need to run that command first. No idea if you even use SNAP.
If you dont need or want it anymore then you should probably remove the driver package.
It would appear to be openrazer-driver so
sudo pacman -Rns openrazer-driver
The headers messages will be partially addressed below but may not longer be applicable if you remove that package.
You also have some very dated and EOL kernels installed.
Please verify your running kernel with
uname -r
If it is 5.10 or 5.4 then please proceed to removing 5.13 as it is dead and gone.
(see kernel.org for an overview)
sudo mhwd-kernel -r linux513
Or if mhwd has trouble then
sudo pacman -Rns linux513
We may need to come back to this due to other steps needed but you probably want to use a more modern kernel like 6.6.
If/when you want to add a newer kernel you can use mhwd-kernel.
sudo mhwd-kernel -i linux66
Your output also shows you need, but do not have, your kernel headers as required by dkms for that driver package.
We would remedy this for any kernel like so:
sudo pacman -Syu linux510-headers
(obviously the same for 54 or 66; linux54-headers)
And whatever newer kernels you find and work … I usually suggest people keep one known working one as well as their newer one. So in your scenario you will probably aim to have 5.10 and 6.6 installed. And remove all others.
Take care to not remove your currently running kernel - reboot into one you intend to keep/use and then remove the others.
But before you reboot
Please make sure to set all of your theming to basic default Breeze (not Breath).
This is most important for SDDM
(System Settings > Appearance & Style > Colors & Themes > Login Screen (SDDM) is the systemsettings path in Plasma 6.1, yours may vary slightly.)
In order to double check on orphans please run the following;
pacman -Qdtq | curl -F 'file=@-' https://0x0.st
Which will create a paste link to share.
that will apply changes from one file to another.