default or selected kernelversion does not have config value CONFIG_JFFS_PROC_FS.
Result is shown for kernelversion 5.15.113

JFFS stats available in /proc filesystem


Linux Kernel Configuration
└─>File systems
└─>Miscellaneous filesystems
└─>JFFS stats available in /proc filesystem
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
Enabling this option will cause statistics from mounted JFFS file systems
to be made available to the user in the /proc/fs/jffs/ directory.