Welcome to the Pi-hole community, iceddonut.
Not sure if this is a Pi-hole issue.
Those above screenshots of yours are not showing Pi-hole's UI, and neither is the log produced by Pi-hole.
In addition, it seems that your are not running the Pi-hole docker image directly, but rather through some kind of process wrapper (presumably, s6 overlay?), as standard Docker Pi-hole wouldn't know or need many of the environment variables shown.
Is it normal for Synology Docker installations to wrap Docker images like that, or is that your own customisation?
The errors you show maybe linked to an older issue, with some leads to the kernel Synology was running on at that time and to the Linux Pluggable Authentication Modules missing some compile-time options, see GitHub for complete coverage.
These have been addressed at the time then, but it's not impossible that they have been reintroduced by some recent changes in Synology or by that process wrapper you are using.