/etc/exim4/conf.d/router/ is in exim4-config 4.76-3ubuntu3.
This file is owned by root:root, with mode 0o755.
..
/etc/exim4/conf.d/router/00_exim4-config_header
/etc/exim4/conf.d/router/100_exim4-config_domain_literal
/etc/exim4/conf.d/router/150_exim4-config_hubbed_hosts
/etc/exim4/conf.d/router/200_exim4-config_primary
/etc/exim4/conf.d/router/300_exim4-config_real_local
/etc/exim4/conf.d/router/400_exim4-config_system_aliases
/etc/exim4/conf.d/router/500_exim4-config_hubuser
/etc/exim4/conf.d/router/600_exim4-config_userforward
/etc/exim4/conf.d/router/700_exim4-config_procmail
/etc/exim4/conf.d/router/800_exim4-config_maildrop
/etc/exim4/conf.d/router/850_exim4-config_lowuid
/etc/exim4/conf.d/router/900_exim4-config_local_user
/etc/exim4/conf.d/router/mmm_mail4root