Looks like it's caused by Fedora's customization. They picked up kernel
lockdown series https://lwn.net/Articles/723653/

If the system is booted using secure boot it puts the kernel in lockdown mode,
which includes disabling all the DebugFSes.

To enable it you have to lift the lockdown:

# sysctl kernel.sysrq=1
<Alt-PrtSc-x> on a physical keyboard; writing to /proc/sysrq-trigger does not
work
[  137.276888] sysrq: SysRq : Disabling Secure Boot restrictions
[  137.276963] Lifting lockdown

What	Removed	Added
Resolution	---	NOTABUG
Status	NEW	RESOLVED