Hey guys. I was facing the same problem (segfault on login) following this guide:
Could fix by installing openssl-1.1 (Arch Linux - openssl-1.1 1.1.1.s-4 (x86_64)) and running cmake with:
cmake -S ~/mangos/zero/server/ -B ~/mangos/zero/build/ -DOPENSSL_ROOT_DIR=/usr/lib/openssl-1.1 -DBUILD_MANGOSD=1 -DBUILD_REALMD=1 -DBUILD_TOOLS=1 -DUSE_STORMLIB=1 -DSCRIPT_LIB_ELUNA=1 -DSCRIPT_LIB_SD3=1 -DPLAYERBOTS=1 -DPCH=1
So
-DOPENSSL_ROOT_DIR=/usr/lib/openssl-1.1
was the fix.