the postgresql11-llvmjit packages are missing from the RH$L repo https://download.postgresql.org/pub/repos/yum/11/redhat/rhel-6-x86_64/ There may be other packages and other repos, but Ihave just come across that oneat the moment.
pgsql-pkg-yum by date:
Соглашаюсь с условиями обработки персональных данных