xsrv VS vouch-proxy

Yes, OpenLDAP installed from this ansible role

It's dead easy to use TCP/SSL instead of UDP to forward logs. Example rsyslog config

I use rsyslog for that since it's the default in Debian. Configuring forwarding is very simple, a single file in /etc/rsyslog.d/forwarding.conf [1]. Note that this setup uses TLS to encrypt messages so you need to create the relevant certificates (I use self-signed certs). Unencrypted TCP or UDP is simpler, but less secure.

preseed.cfg contains a few basic options needed to setup the OS [1]

I do this with https://github.com/nodiscc/xsrv/tree/master/roles/openldap + https://github.com/nodiscc/xsrv/tree/master/roles/samba. It's just a standalone samba server + LDAP auth for users, no DC or anything like that, so I'm not sure this is what you're looking for.

This ansible role (check the tasks/ directory) gives a good breakdown of what is needed to setup a basic LDAP server and authentication service

I use samba in standalone mode with or without LDAP auth https://github.com/nodiscc/xsrv/tree/master/roles/samba

Look into vouch proxy

Vouch proxy is designed for this usage: https://github.com/vouch/vouch-proxy I don't think there are any nice UIs to configure it though so you'll need to be familiar with running it yourself.

Not sure this is a "best practice", but it lets me keep control of the Ingress resources inside their YAML configs. I've also layered Vouch Proxy into the ingress configurations to require SSO/MFA auth to access the resources behind the Ingress. Cloudflare has the ability to do this, but I found it cumbersome to keep track of the configs outside the K8s cluster.

I've used vouch proxy for my own stuff previously, before more recently moving to Cloudflare Access. vouch can be slightly janky at times to get working right, but once set up, it's been solid.

For example: nginx -> Vouch proxy -> KeyCloak -> Jellyfin

While this works, we were hoping to make access a bit easier with say an OpenID Connect SSO and reverse-proxy solution. I've seen Vouch Proxy, https://github.com/vouch/vouch-proxy which is really just SSO on top of nginx, but I'm wondering if there's a simpler way to do this.

You seem to be quite knowledgeable and a minimal provider with just the bare minimum would suffice for you. Have a look at Vouch Proxy, it does one thing and it does it well.