

Nice, good on you! Migrating your services/containers to a dedicated server instead of running them on a overwhelmingly underpowered Synology NAS is going to be a game changer.
I also have a Synology NAS, but nowadays only really use it for NFS/Samba storage and a S3 service (Garage) running on it to provide network storage to all my other services running on my mini pc.

Yeah faced that issue a couple of weeks ago as well after updating Podman. It didn’t allow me to set container individual UID/GID mappings or UserNS when running in a pod, so I just took them out of the pod as I couldn’t be bothered and run them as separate containers in the same network. Works just as good.
You just have to make sure to move the PublishPort block from the pod quadlet to the gluetun container (for all the containers which route their traffic through gluetun, i.e. which have ‘Network=container: gluetun’ set). This should solve the problem and still allows you to use UserNS or UID/GID mappings on the containers. No disadvantages so far, you just lose the convenience of stopping/starting all the containers at once through the pod. But I’d rather take this ‘inconvenience’ than troubleshooting for days how to make it work with a pod again.