default or selected kernelversion does not have config value CONFIG_IEEE80211_CRYPT_WEP.
Result is shown for kernelversion 5.4.123

IEEE 802.11 WEP encryption (802.1x)

modulename: ieee80211_crypt_wep.ko

configname: CONFIG_IEEE80211_CRYPT_WEP

Linux Kernel Configuration
└─>Networking
└─>IEEE 802.11 WEP encryption (802.1x)
In linux kernel since version 2.6.14 (release Date: 2005-10-27)  
Include software based cipher suites in support of IEEE
802.11's WEP. This is needed for WEP as well as 802.1x.

This can be compiled as a modules and it will be called
"ieee80211_crypt_wep".

source code: