I suggest to check out the systemd article in the arch wiki and troubleshoot. There is a process still running that avoids your system to shut down. You need to figure out which one.
https://wiki.archlinux.org/title/Systemd#Troubleshooting
Please avoid this, as it can corrupt a file system, and read
The Linux kernel authors have provided a very nice feature of issuing low-level commands to the kernel directly, regardless of the state the system is in. This is called the “Magic SysRq Key”, because these commands are issued by pressing the SysRq key on the keyboard (if you can’t find it, typically, it shares the same physical key as the Print Screen key, but on some laptops it can be elsewhere).
A common use is to reboot when the computer freezes and becomes unresponsive due to some software…