@Botanist-Gr7een thank you for such qualified post it’s always a joy not to ask silly questions 
you already isolated the problem, we only need to find the root cause.
This step is definitely the blocker now:
for a reason I don’t understand from the config you posted your CODE connects to nc_app container directly and this fails because it doesn’t have valid certificate (which is expected in case of “TLS offloading” like in your case).
the connection from CODE must reach your reverseproxy at ipv4_address: 172.21.0.2
This might help
- Probably DNS help with NC Docker + Collabora + Wireguard tunnel - #5 by wwe
if I’m not wrong adding the alias to yournpm_proxywill fix the issue. if not we must troubleshoot why CODE connects tonc_appand notnpm_proxy
It is not related to the problem but community microservices image doesn’t utilize PUID variables (maybe upstream consume it partially)… you can look at Nextcloud docker-compose setup with notify_push (2024) to learn how to make the whole Nextcloud container running as specific user.
for my education
- why do you use fixed ip addresses - Docker is expected to manage them on it’s own - is it required for
npm_proxy? - what is the content of
/docker-entrypoint-hooks.d/post-installation/richdocuments.sh