/etc/apache2/mods-available/proxy_balancer.load is in apache2 2.4.25-3+deb9u6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | # Depends: proxy alias slotmem_shm
LoadModule proxy_balancer_module /usr/lib/apache2/modules/mod_proxy_balancer.so
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