As that page is referring to very old versions of Linux and GCC, it should be considered out-of-date. The /cvmfs/sft.cern.ch/lcg/views/LCG_101/x86_64-centos7-gcc11-opt should work fine as is the latest LCG release, though it comes with Geant4 10.7.2 only.
For the MIT-MAGIC-Cookie issue, have you tried the suggestions linked in this post?