default or selected kernelversion does not have config value CONFIG_RTLLIB_CRYPTO_WEP.
Result is shown for kernelversion 6.9.9

Support for rtllib WEP crypto

modulename: rtllib_crypt_wep.ko

configname: CONFIG_RTLLIB_CRYPTO_WEP

Linux Kernel Configuration
└─>Device Drivers
└─>Staging drivers
└─>Support for rtllib WEP crypto
In linux kernel since version 3.1 (release Date: 2011-10-24)  
WEP crypto driver for rtllib.

If you enabled RTLLIB, you want this.
Adds support for the (now weak) Wired Equivalent Privacy
(WEP) crypto protocol for wireless cards.
NOTE: This protocol is now considered insecure.

source code: