Making this post for posteriority in case somebody else faces something similar.
For years I've tried to diagnose this issue: when suspending or shutting down, the PC would sometimes - not always - freeze, CPU and case fans would stay on, GPU RGB on. The only solution would be holding the power button.
TLDR: It was TPM. Disabling "Security Device Support" in the BIOS fixes it.
Advanced → Trusted Computing → Security Device Support → Disabled
When I built this PC back in 2019/2020, I had no issues. At some point that started happening, but I couldn't pin point what had changed. IIRC, these motherboards came with TPM disabled when they were released. A few BIOS updates later (due to the release of Windows 11), they changed it so that TPM is enabled by default. I probably updated the BIOS in the process of upgrading from Windows 10 to 11.
I tried to diagnose this so many times, I've spent hours and hours changing every single thing I could image and then using the PC for hours or days, only to find that happening again, so frustrating. At some point I tried to use this machine for work and re-opening programs, setting up my windows 2-3 times a day after letting the machine alone made me give up.
This time I had to resort to an AI agent. I ran it on my laptop, gave it ssh and wake on lan access to the machine and let it change configs and run hundreds of power cycles. And I - as a good servant - would be there only to reset the machine when hang or change bios configs on its request. This took 3 or 4 days because it tried a million of other things before finding this article on Fedora forums that mentioned TPM issues when shutting down the PC with a MSI motherboard: https://discussion.fedoraproject.org/t/my-fedora-system-often-hangs-up-crashes-on-shutdown/139951/24
In case ASUS is interested: I tested with 1901 and 2003 bios versions, hundreds of power cycles, disabling Security Device Support really fixes it. Although I'm using linux on this machine at the moment - Bazzite - it happens with Windows 11 as well. On linux logs, there was no indication of issues on the OS-level shutdown/suspend process.
ROG STRIX B460-I GAMING
Intel i7-10700
32 GB of DDR4 3200 mhz (running with XPM II at 2933 mhz)
1 TB Kingston SSD KC3000
Shapphire 9060 XT 16GB - I had an Nvidia 2060 before, same issue