I run, vikunja on a domain via cloudflare this was using ip and cloudlfare proxy.
when arriving at the local server it had nginx serve vikunja on reverse proxy. All was working well.
Note vikunja runs in docker on the same server that runs nginx natively.
I have recently starting to migrate things to a cloudflare tunnel, when tunneling the domain either to localhost:[port] straight to the app, or localhost:80 and reverse proxy though nginx Vikunja only gets served when outside of the localnetwork.
work laptop that uses work VPN: it gets served
Home pc on same netwotrk: the site can’t be reached
Mobile phone no wifi no VPN: it gets served
Mobile phone no wifi but VPN into local: the site can’t be served
other apps on the same tunnel can be reached internal and external via the same domain