I have a Thinkpad C13 with Arch Linux installed.

When any power events occur (shutdown reboot sleep) the computer appears to successfully follow the shutdown procedure killing all the services until the last line is 'Powering off' at that point it just freezes and no longer responds to input. I have left it in that state for over an hour to confirm it is not just slow.

Commands I used to shutdown or reboot:
- shutdown -h now
- poweroff
- reboot

I tried the following grub boot options:
- iommu=soft
- acpi=force
- apm=power_off
- no apic
- irqpoll

Result of lspci -nnvv: https://pastebin.com/qn1Qw0NJ

How exactly did you install ArchLinux on that?

I use halt -p to shutdown & switch off Linux, it is basically the same as poweroff, but always works for me.

I ran firmware utility script from mrchromebox.tech to configure UEFI. Then used a arch iso on a usb drive.

OK. Just wanted to make sure you weren't still running ChromeOS.
Take a look at the journal, with 'journalctl'.
(Read the man page, there are options to stem the flood of log messages).
Look for what gets logged during failed sleep/hibernation/poweroff events. Meaning, check the time stamps. journalctl has an option to make them human readable.
Don't just flood us with everything since the beginning of time please.

Result from 'journalctl -b -1 -r': https://pastebin.com/ZCkcZh89

If something untoward happened on Feb 03 08:58:09, I cannot see it.
Maybe it's "an ACPI thing", but I think the journal would have logged something.
What else did your searches & troubleshooting bring meanwhile?

Having a chrome book with antiX installed myself.

Have you tried another kernel?

I was running Kubuntu on a Asus Chromebook and did not have any issues with powering it off.
May want to try a bootable live distro and see if it has the same issue to rule out hardware, but it just mght be an Arch thing.

Have you tried the LTS kernel?

I go through this with Fedora on occasion on my ThinkPads, after an update it will hang on boot or shutdown, going back to the previous kernel works.

Give the LTS kernel a shot, with that laptop there's nothing you're going to lose by using the LTS kernel and it's (theoretically) been tested better.